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Document And Entity Information - shares	6 Months Ended
Document And Entity Information - shares	Jun. 30, 2014	Jul. 31, 2014
Document and Entity Information [Abstract]
Entity Registrant Name	BIOCRYST PHARMACEUTICALS INC
Document Type	10-Q
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		71,756,307
Amendment Flag	false
Entity Central Index Key	0000882796
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Well-known Seasoned Issuer	No
Document Period End Date	Jun. 30, 2014
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	Q2

Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Jun. 30, 2014	Dec. 31, 2013
Assets
Cash and cash equivalents	$ 121,519	$ 21,164
Restricted cash	150	151
Investments	10,589	16,891
Receivables	897	2,115
Prepaid expenses and other current assets	5,020	1,725
Deferred collaboration expense	75	75
Total current assets	138,250	42,121
Investments	602	2,582
Furniture and equipment, net	216	306
Deferred collaboration expense	207	237
Other assets	2,700	3,620
Total assets	141,975	48,866
Liabilities and Stockholders’ Equity
Accounts payable	2,360	4,174
Accrued expenses	7,309	5,742
Interest payable	3,786	3,867
Deferred collaboration revenue	1,482	1,473
Non-recourse notes payable	30,000	0
Total current liabilities	44,937	15,256
Deferred collaboration revenue	4,144	4,736
Foreign currency derivative	2,805	0
Non-recourse notes payable	0	30,000
Stockholders’ equity:
Preferred stock, $0.001 par value; shares authorized — 5,000; no shares issued and outstanding	0	0
Common stock, $0.01 par value: shares authorized — 200,000; shares issued and outstanding — 71,718 in 2014 and 59,092 in 2013	717	591
Additional paid-in capital	536,864	420,988
Accumulated other comprehensive income	3	4
Accumulated deficit	(447,495)	(422,709)
Total stockholders’ equity (deficit)	90,089	(1,126)
Total liabilities and stockholders’ equity	$ 141,975	$ 48,866

Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - $ / shares shares in Thousands	Jun. 30, 2014	Dec. 31, 2013
Preferred stock par value (in Dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000	5,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in Dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000
Common stock, shares issued	71,718	59,092
Common stock, shares outstanding	71,718	59,092

Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenues
Royalty revenue	$ 125	$ 110	$ 1,946	$ 2,034
Collaborative and other research and development	1,341	711	2,978	2,341
Total revenues	1,466	821	4,924	4,375
Expenses
Research and development	11,067	11,527	20,250	18,742
General and administrative	2,013	1,432	3,601	3,010
Royalty	5	4	78	81
Total operating expenses	13,085	12,963	23,929	21,833
Loss from operations	(11,619)	(12,142)	(19,005)	(17,458)
Interest and other income	19	21	36	54
Interest expense	(1,225)	(1,165)	(2,467)	(2,345)
Gain (loss) on foreign currency derivative	(1,824)	1,114	(3,350)	3,071
Net loss	$ (14,649)	$ (12,172)	$ (24,786)	$ (16,678)
Basic and diluted net loss per common share (in Dollars per share)	$ (0.23)	$ (0.23)	$ (0.40)	$ (0.32)
Weighted average shares outstanding (in Shares)	63,647	53,468	61,629	52,277
Unrealized gain (loss) on investments	$ 1	$ (9)	$ (1)	$ (21)
Comprehensive loss	$ (14,648)	$ (12,181)	$ (24,787)	$ (16,699)

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Operating activities
Net loss	$ (24,786)	$ (16,678)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	97	183
Stock-based compensation expense	5,129	2,521
Amortization of debt issuance costs	220	220
Change in fair value of foreign currency derivative	3,350	(3,071)
Changes in operating assets and liabilities:
Receivables	1,218	3,538
Prepaid expenses and other assets	(408)	(53)
Deferred collaboration expense	30	5,106
Accounts payable and accrued expenses	(247)	(7,072)
Interest payable	(81)	1,660
Deferred collaboration revenue	(583)	(447)
Net cash used in operating activities	(16,061)	(14,093)
Investing activities
Acquisitions of furniture and equipment	(7)	(26)
Change in restricted cash	1	(1,821)
Purchases of investments	(12,651)	(369)
Sales and maturities of investments	20,900	6,820
Net cash provided by investing activities	8,243	4,604
Financing activities
Sale of common stock, net	106,600	5,171
Exercise of stock options	4,145	346
Employee stock purchase plan sales	128	68
(Payment) receipt of foreign currency derivative collateral	(2,700)	2,780
Net cash provided by financing activities	108,173	8,365
Increase (decrease) in cash and cash equivalents	100,355	(1,124)
Cash and cash equivalents at beginning of period	21,164	20,891
Cash and cash equivalents at end of period	$ 121,519	$ 19,767

Note 1 - Significant Accounting Policies

6 Months Ended

Jun. 30, 2014

Accounting Policies [Abstract]

Significant Accounting Policies [Text Block]

Note 1 — Significant Accounting Policies

The Company

BioCryst Pharmaceuticals, Inc. (the “Company”) is a biotechnology company that designs, optimizes and develops novel small molecule drugs that block key enzymes involved in the pathogenesis of diseases. The Company focuses on rare diseases in which unmet medical needs exist and that are aligned with its capabilities and expertise. The Company was incorporated in Delaware in 1986 and its headquarters is located in Durham, North Carolina. The Company integrates the disciplines of biology, crystallography, medicinal chemistry and computer modeling to discover and develop small molecule pharmaceuticals through the process known as structure-guided drug design. BioCryst has incurred losses and negative cash flows from operations since inception.

Based on its current operating plans, the Company expects it has sufficient liquidity, with its existing cash and investments of $132,860, to continue its planned operations beyond fiscal 2015. The Company’s liquidity needs, and ability to address those needs, will largely be determined by the success of its product candidates and key development and regulatory events in the future. In order to continue its operations beyond 2016 it will need to: (1) successfully secure or increase U.S. Government funding of its programs; (2) out-license rights to certain of its product candidates, pursuant to which the Company would receive cash milestones; (3) raise additional capital through equity or debt financings or from other sources; (4) obtain product candidate regulatory approvals, which would generate revenue and cash flow; (5) reduce spending on one or more research and development programs; and/or (6) restructure operations. The Company will continue to incur operating losses and negative cash flows until revenues reach a level sufficient to support ongoing operations.

Basis of Presentation

Beginning in March 2011, the consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, JPR Royalty Sub LLC (“Royalty Sub”). Royalty Sub was formed in connection with a $30,000 financing transaction the Company completed on March 9, 2011. See Note 4, Royalty Monetization, for a further description of this transaction. All intercompany transactions and balances have been eliminated.

The Company’s consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) for interim financial reporting and the instructions to Form 10-Q and do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. Such financial statements reflect all adjustments that are, in management’s opinion, necessary to present fairly, in all material respects, the Company’s consolidated financial position, results of operations, and cash flows. There were no adjustments other than normal recurring adjustments.

These financial statements should be read in conjunction with the financial statements for the year ended December 31, 2013 and the notes thereto included in the Company’s 2013 Annual Report on Form 10-K. Interim operating results are not necessarily indicative of operating results for the full year. The balance sheet as of December 31, 2013 has been derived from the audited consolidated financial statements included in the Company’s most recent Annual Report on Form 10-K.

Reclassifications

In the first quarter of 2014, the Company changed its classification of legal costs associated with its patents. This change resulted in $201 and $397 of legal expenses being reclassified from research and development expense to general and administrative expense for the three and six months ended June 30, 2013, respectively. This reclassification had no effect on previously reported total operating expenses or net loss amounts.

Cash and Cash Equivalents

The Company generally considers cash equivalents to be all cash held in commercial checking accounts, money market accounts or investments in debt instruments with maturities of three months or less at the time of purchase. The carrying value of cash and cash equivalents approximates fair value due to the short-term nature of these items.

Restricted Cash

Restricted cash as of June 30, 2014 represents cash the Company is required to maintain in an interest bearing certificate of deposit to serve as collateral for a corporate credit card program.

Investments

The Company invests in high credit quality investments in accordance with its investment policy, which is designed to minimize the possibility of loss. The objective of the Company’s investment policy is to ensure the safety and preservation of invested funds, as well as maintaining liquidity sufficient to meet cash flow requirements. The Company places its excess cash with high credit quality financial institutions, commercial companies, and government agencies in order to limit the amount of its credit exposure. Per its policy, the Company is able to invest in marketable debt securities that may consist of U.S. Government and government agency securities, money market and mutual fund investments, municipal and corporate notes and bonds, commercial paper and asset or mortgage-backed securities, among others. The Company’s investment policy requires it to purchase high-quality marketable securities with a maximum individual maturity of three years and requires an average portfolio maturity of no more than 18 months. Some of the securities the Company invests in may have market risk. This means that a change in prevailing interest rates may cause the principal amount of the investment to fluctuate. To minimize this risk, the Company schedules its investments with maturities that coincide with expected cash flow needs, thus avoiding the need to redeem an investment prior to its maturity date. Accordingly, the Company does not believe it has a material exposure to interest rate risk arising from its investments. Generally, the Company’s investments are not collateralized. The Company has not realized any significant losses from its investments.

The Company classifies all of its investments as available-for-sale. Unrealized gains and losses on investments are recognized in comprehensive income/(loss), unless an unrealized loss is considered to be other than temporary, in which case the unrealized loss is charged to operations. The Company periodically reviews its investments for other than temporary declines in fair value below cost basis and whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. The Company believes the individual unrealized losses represent temporary declines primarily resulting from interest rate changes. Realized gains and losses are reflected in interest and other income in the Consolidated Statements of Comprehensive Loss and are determined using the specific identification method with transactions recorded on a settlement date basis. Investments with original maturities at date of purchase beyond three months and which mature at or less than 12 months from the balance sheet date are classified as current. Investments with a maturity beyond 12 months from the balance sheet date are classified as long-term. At June 30, 2014, the Company believes that the costs of its investments are recoverable in all material respects.

The following tables summarize the fair value of the Company’s investments by type. The estimated fair value of the Company’s fixed income investments are classified as Level 2 in the fair value hierarchy as defined in U.S. GAAP. These fair values are obtained from independent pricing services which utilize Level 2 inputs.

	June 30, 2014
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Corporate debt securities	$	2,278	$	14	$	2	$	—	$	2,294
Commercial paper		8,896		—		1		—		8,897
Total investments	$	11,174	$	14	$	3	$	—	$	11,191

	December 31, 2013
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Obligations of U.S. Government and its agencies	$	4,899	$	1	$	1	$	—	$	4,901
Corporate debt securities		8,528		47		2		1		8,576
Commercial paper		5,994		—		2		—		5,996
Total investments	$	19,421	$	48	$	5	$	1	$	19,473

The following table summarizes the scheduled maturity for the Company’s investments at June 30, 2014 and December 31, 2013.

	2014		2013
Maturing in one year or less	$	10,589	$	16,891
Maturing after one year through two years		602		2,582
Total investments	$	11,191	$	19,473

Receivables

Receivables are recorded for amounts due to the Company related to reimbursable research and development costs from the U.S. Department of Health and Human Services or royalty receivables from Shionogi & Co. Ltd. At June 30, 2014 and December 31, 2013, the Company had the following receivables.

	June 30, 2014
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	236	$	600	$	836
Shionogi & Co. Ltd.		61		—		61
Total receivables	$	297	$	600	$	897

	December 31, 2013
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	90	$	1,573	$	1,663
Shionogi & Co. Ltd.		452		—		452
Total receivables	$	542	$	1,573	$	2,115

Monthly invoices are submitted to the U.S. Department of Health and Human Services related to reimbursable research and development costs. The Company is also entitled to monthly reimbursement of indirect costs based on rates stipulated in the underlying contract. The Company’s calculations of its indirect cost rates are subject to audit by the federal government.

Patents and Licenses

The Company seeks patent protection on internally developed processes and products. All patent related legal costs are expensed to general and administrative expenses when incurred as recoverability of such expenditures is uncertain.

Accrued Expenses

The Company generally enters into contractual agreements with third-party vendors who provide research and development, manufacturing, and other services in the ordinary course of business. Some of these contracts are subject to milestone-based invoicing and services are completed over an extended period of time. The Company records liabilities under these contractual commitments when it determines an obligation has been incurred, regardless of the timing of the invoice. This process involves reviewing open contracts and purchase orders, communicating with applicable Company personnel to identify services that have been performed on its behalf and estimating the level of service performed and the associated cost incurred for the service when the Company has not yet been invoiced or otherwise notified of actual cost. The majority of service providers invoice the Company monthly in arrears for services performed. The Company makes estimates of accrued expenses as of each balance sheet date in its financial statements based on the facts and circumstances. The Company periodically confirms the accuracy of its estimates with the service providers and makes adjustments if necessary. Examples of estimated accrued expenses include:

•

fees paid to Clinical Research Organizations (“CROs”) in connection with preclinical and toxicology studies and clinical trials;

•

fees paid to investigative sites in connection with clinical trials;

•

fees paid to contract manufacturers (“CMOs”) in connection with the production of our raw materials, drug substance and drug products; and

•

professional fees.

The Company bases its expenses related to clinical trials on its estimates of the services received and efforts expended pursuant to contracts with multiple research institutions and clinical research organizations that conduct and manage clinical trials, including manufacturing drug substance, on the Company’s behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows. Payments under some of these contracts depend on factors such as the successful enrollment of patients and the completion of clinical trial milestones. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. Accrued expenses as of June 30, 2014 and December 31, 2013 included $1,392 and $2,210, respectively, of research and development costs.

Income Taxes

The liability method is used in the Company’s accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on differences between financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse.

Accumulated Other Comprehensive (Loss) Income

Accumulated other comprehensive (loss) income is comprised of unrealized gains and losses on investments available-for-sale and is disclosed as a separate component of stockholders’ equity. No reclassifications out of accumulated other comprehensive (loss) income were recorded during the six months ended June 30, 2014 and 2013.

Revenue Recognition

The Company recognizes revenues from collaborative and other research and development arrangements and product sales. Revenue is realized or realizable and earned when all of the following criteria are met: (i) persuasive evidence of an arrangement exists; (ii) delivery has occurred or services have been rendered; (iii) the seller’s price to the buyer is fixed or determinable; and (iv) collectability is reasonably assured.

Collaborative and Other Research and Development Arrangements and Royalties

Revenue from license fees, royalty payments, milestone payments, and research and development fees is recognized as revenue when the earnings process is complete and the Company has no further continuing performance obligations or the Company has completed the performance obligations under the terms of the agreement. Fees received under licensing agreements that are related to future performance are deferred and recognized over an estimated period determined by management based on the terms of the agreement and the products licensed. In the event a license agreement contains multiple deliverables, the Company evaluates whether the deliverables are separate or combined units of accounting. Revisions to revenue or profit estimates as a result of changes in the estimated revenue period are recognized prospectively.

Under certain of our license agreements, the Company receives royalty payments based upon our licensees’ net sales of covered products. The Company recognizes royalty revenues when it can reliably estimate such amounts and collectability is reasonably assured.

Reimbursements received for direct out-of-pocket expenses related to research and development costs are recorded as revenue in the Consolidated Statements of Comprehensive Loss rather than as a reduction in expenses. Milestone payments are recognized as revenue upon the achievement of specified events if (1) the milestone is substantive in nature and the achievement of the event was not reasonably assured at the inception of the agreement and (2) the fees are non-refundable and non-creditable. Any milestone payments received prior to satisfying these criteria are recorded as deferred revenue. Under the Company’s contracts with the U.S. Department of Health and Human Services, (“BARDA/HHS”), and the National Institute of Allergy and Infectious Diseases (“NIAID/HHS”), revenue is recognized as reimbursable direct and indirect costs are incurred. The Company’s advanced development contract with BARDA/HHS for the development of peramivir expired on June 30, 2014 according to its terms.

Product Sales

Product sales are recognized net of estimated allowances, discounts, sales returns, chargebacks and rebates.

The Company recorded the following revenues for the three and six months ended June 30, 2014 and 2013:

	Three Months				Six Months
	2014		2013		2014		2013
Royalty revenue	$	125	$	110	$	1,946	$	2,034
Collaborative and other research and development revenues:
U.S. Department of Health and Human Services		1,045		415		2,386		1,749
Shionogi (Japan)		296		296		592		592

Total revenues	$	1,466	$	821	$	4,924	$	4,375

Research and Development Expenses

The Company’s research and development costs are charged to expense when incurred. Research and development expenses include all direct and indirect development costs related to the development of the Company’s portfolio of product candidates. Advance payments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized. Such amounts are recognized as expense when the related goods are delivered or the related services are performed. Research and development expenses include, among other items, personnel costs, including salaries and benefits, manufacturing costs, clinical, regulatory, and toxicology services performed by CROs and CMOs, materials and supplies, and overhead allocations consisting of various administrative and facilities related costs. Most of the Company’s manufacturing and clinical and preclinical studies are performed by third-party CROs and CMOs. Costs for studies performed by CROs and CMOs are accrued by the Company over the service periods specified in the contracts and estimates are adjusted, if required, based upon the Company’s on-going review of the level of services actually performed.

Additionally, the Company has license agreements with third parties, such as Albert Einstein College of Medicine of Yeshiva University (“AECOM”), Industrial Research, Ltd. (“IRL”), and the University of Alabama at Birmingham (“UAB”), which require fees related to sublicense agreements or maintenance fees. The Company expenses sublicense payments as incurred unless they are related to revenues that have been deferred, in which case the expenses are deferred and recognized over the related revenue recognition period. The Company expenses maintenance payments as incurred.

Deferred collaboration expenses represent sub-license payments, paid to the Company’s academic partners upon receipt of consideration from various commercial partners, and other consideration paid to our academic partners for modification to existing license agreements. These deferred expenses would not have been incurred without receipt of such payments or modifications from the Company’s commercial partners and are being expensed in proportion to the related revenue being recognized. The Company believes that this accounting treatment appropriately matches expenses with the associated revenue.

Stock-Based Compensation

All share-based payments, including grants of stock option awards and restricted stock awards, are recognized in the Company’s Consolidated Statements of Comprehensive Loss based on their fair values. The fair value of stock option awards is estimated using the Black-Scholes option pricing model. The fair value of restricted stock awards is based on the grant date closing price of the common stock. Stock-based compensation cost is recognized as expense on a straight-line basis over the requisite service period of the award. For stock option awards with performance conditions, the Company recognizes compensation expense at the time whereby the underlying performance condition has been determined to have occurred.

Interest Expense and Deferred Financing Costs

Interest expense for the three months and six months ended June 30, 2014 and 2013 was $1,225 and $1,165, respectively, and $2,467 and $2,345, respectively, and relates to the issuance of the PhaRMA Notes (defined in Note 4). Costs directly associated with the issuance of the PhaRMA Notes have been capitalized and are included in other current assets on the Consolidated Balance Sheets. These costs are being amortized to interest expense over the term of the PhaRMA Notes using the effective interest rate method. Amortization of deferred financing costs included in interest expense was $110 for each of the three months ended June 30, 2014 and 2013, and $220 for each of the six months ended June 30, 2014 and 2013.

Currency Hedge Agreement

In connection with the issuance by Royalty Sub of the PhaRMA Notes, the Company entered into a Currency Hedge Agreement (defined in Note 4) to hedge certain risks associated with changes in the value of the Japanese yen relative to the U.S. dollar. The Currency Hedge Agreement does not qualify for hedge accounting treatment; therefore, mark-to-market adjustments are recognized in the Company’s Consolidated Statements of Comprehensive Loss. Cumulative mark-to-market adjustments for the six months ended June 2014 and 2013 resulted in a loss of $3,350 and a gain of $3,071, respectively. Mark-to-market adjustments are determined by a third party pricing model that uses quoted prices in markets that are not actively traded and for which significant inputs are observable directly or indirectly, representing Level 2 in the fair value hierarchy as defined by U.S. GAAP. The Company is also required to post collateral in connection with the mark-to-market adjustments based on thresholds defined in the Currency Hedge Agreement. As of June 30, 2014, $2,700 of hedge collateral was posted under the agreement. No hedge collateral was posted under the agreement as of December 31, 2013.

Net Loss Per Share

Net loss per share is based upon the weighted average number of common shares outstanding during the period. Diluted loss per share is equivalent to basic net loss per share for all periods presented herein because common equivalent shares from unexercised stock options and common shares expected to be issued under the Company’s employee stock purchase plan were anti-dilutive. The calculation of diluted earnings per share for the three months ended June 30, 2014 and 2013 does not include 5,038 and 978, respectively, of such potential common shares, as their impact would be anti-dilutive. The calculation of diluted earnings per share for the six months ended June 30, 2014 and 2013 does not include 5,123 and 852, respectively, of such potential common shares, as their impact would be anti-dilutive.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires the Company to make estimates and assumptions that affect the amounts reported in the financial statements. Actual results could differ from those estimates.

Concentration of Market Risk

The reimbursement of peramivir and BCX4430 development expenses is a significant source of revenue and one which has an underlying cash flow stream. This revenue and cash flow is earned under fixed fee contracts and cost-plus-fixed-fee contracts with BARDA/HHS and NIAID/HHS. The Company relies on BARDA/HHS and NIAID/HHS to reimburse predominantly all of the development costs for its peramivir and BCX4430 programs, respectively. Accordingly, reimbursement of these expenses represents a significant portion of the Company’s collaborative and other research and development revenues. The completion and/or termination of these programs/collaborations could negatively impact the Company’s future Consolidated Statements of Comprehensive Loss and Cash Flows.

In addition, the Company also recognizes royalty revenue from the net sales of RAPIACTA®; however, the underlying cash flow from these royalty payments goes directly to pay the interest, and then the principal, on the non-recourse notes payable. Payment of the interest and the ultimate repayment of principal of these notes will be entirely funded by future royalty payments derived from net sales of RAPIACTA®. At June 30, 2014, there was a significant underpayment of interest on the PhaRMA Notes, which if unpaid at September 1, 2014, will constitute an event of default under the PhaRMA Notes. Based upon information available at June 30, 2014, the Company expects the RAPIACTA® royalty stream from Shionogi & Co. (“Shionogi”), the Company’s partner in Japan, to be insufficient to pay the accrued interest in arrears on the non-recourse PhaRMA Notes by the September 1, 2014 payment date. If the royalty stream is insufficient to pay the interest in arrears, an event of default will occur with respect to the PhaRMA Notes. Accordingly, the Company has classified the PhaRMA Notes and related accrued interest as current liabilities on its balance sheet. If an event of default were to occur under the PhaRMA Notes, the holders of the PhaRMA Notes may pursue acceleration of the PhaRMA Notes, foreclose on the collateral securing the PhaRMA Notes and the Company’s equity interest in Royalty Sub and exercise other remedies available to them under the indenture in respect of the PhaRMA Notes. In such event, the Company may not realize the benefit of future royalty payments that might otherwise accrue to the Company following repayment of the PhaRMA Notes and it might otherwise be adversely affected. Due to the non-recourse nature of the PhaRMA Notes, in the event of any potential acceleration or foreclosure, the Company believes the primary impact to the Company would be the loss of future royalty payments from Shionogi and legal costs associated with retiring the PhaRMA Notes. In addition, the Company may incur costs associated with liquidating a related currency hedge agreement, which would no longer be required in the event of foreclosure or if the PhaRMA Notes cease to be outstanding. As the PhaRMA Notes are obligations of Royalty Sub, the Company does not currently expect an event of default on the PhaRMA Notes to have a significant impact on the Company’s future results of operations or cash flows.

The Company’s drug development activities are performed by a limited group of third party vendors. If any of these vendors were unable to perform their services, this could significantly impact the Company’s ability to complete its drug development activities.

Credit Risk

Cash equivalents and investments are financial instruments which potentially subject the Company to concentration of risk to the extent recorded on the Consolidated Balance Sheets. The Company deposits excess cash with major financial institutions in the United States. Balances may exceed the amount of insurance provided on such deposits. The Company believes it has established guidelines for investment of its excess cash relative to diversification and maturities that maintain safety and liquidity. To minimize the exposure due to adverse shifts in interest rates, the Company maintains a portfolio of investments with an average maturity of approximately 24 months or less. The majority of the Company’s receivables are due from the U.S. Government, for which there is no assumed credit risk.

Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standard Update ("ASU") 2014-09 – Revenue from Contracts with Customers, which provides a single, comprehensive revenue recognition model for all contracts with customers. The core principal of this ASU is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This ASU also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. This ASU is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2016. Early adoption is not permitted and companies can transition to the new standard under the full retrospective method or the modified retrospective method. The Company is currently evaluating the impact this ASU will have on its consolidated financial statements.

In June 2014, the Financial Accounting Standards Board issued ASU 2014-12 – Compensation – Stock Compensation: Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could be Achieved after the Requisite Service Period, which provides explicit guidance for the accounting treatment for these types of awards. The ASU requires that a performance target that affects vesting and that could be achieved after the requisite service period be treated as a performance condition. As such, the performance target should not be reflected in estimating the grant-date fair value of the award. This update is effective for annual periods and interim periods within those annual periods beginning after December 15, 2014. Early adoption is permitted. The Company does not expect this ASU will have a material impact on its consolidated financial statements.

Note 2 - Stock-Based Compensation

6 Months Ended

Jun. 30, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

Note 2 — Stock-Based Compensation

As of June 30, 2014, the Company had two stock-based employee compensation plans, the Stock Incentive Plan (“Incentive Plan”) and the Employee Stock Purchase Plan (“ESPP”), both which were amended and restated in March 2014 and approved by the Company’s stockholders in May 2014. Stock-based compensation expense of $5,129 ($5,020 of expense related to the Incentive Plan and $109 of expense related to the ESPP) was recognized during the first six months of 2014, while $2,521 ($2,479 of expense related to the Incentive Plan and $42 of expense related to the ESPP) was recognized during the first six months of 2013.

There was approximately $11,182 of total unrecognized compensation cost related to non-vested stock option awards and restricted stock awards granted by the Company as of June 30, 2014. That cost is expected to be recognized as follows: $2,548 during the remainder of 2014, $3,688 in 2015, $2,619 in 2016, $2,153 in 2017 and $174 in 2018. In addition, the Company has outstanding performance-based stock options for which no compensation expense is recognized until achievement of the performance condition has been determined to have occurred.

Stock Incentive Plan

The Company grants stock option awards and restricted stock awards to its employees, directors, and consultants under the Incentive Plan. Under the Incentive Plan, stock option awards are granted with an exercise price equal to the market price of the Company’s stock at the date of grant. Stock option awards granted to employees generally vest 25% each year until fully vested after four years. In January 2013, the Company made retention grants of stock option awards and restricted stock awards. These awards vest 50% each year until fully vested after two years. In August 2013, the Company issued 1,032 performance-based stock options that vest upon successful completion of specific development milestones. Following successful completion of the OPuS-1 clinical trial, 25% of the outstanding performance awards vested. As of June 30, 2014 and based on the information available at that time, 75% of the August 2013 performance awards remain unvested and no compensation expense has been recognized for this portion of the performance-based grant awards. Stock option awards granted to non-employee directors of the Company generally vest monthly over one year. All stock option awards have contractual terms of 5 to 10 years. The vesting exercise provisions of all awards granted under the Incentive Plan are subject to acceleration in the event of certain stockholder-approved transactions, or upon the occurrence of a change in control as defined in the Incentive Plan.

Related activity under the Incentive Plan is as follows:

	Awards Available			Options Outstanding			Weighted Average Exercise Price
Balance December 31, 2013		1,082			8,986		$	4.99
Plan amendment		3,750			—			—
Restricted stock awards granted		(593	)		—			—
Restricted stock awards cancelled		—			—			—
Stock option awards granted		(505	)		505			10.28
Stock option awards exercised		—			(1,034	)		4.90
Stock option awards cancelled		88			(88	)		8.83
Balance June 30, 2014		3,822			8,369		$	5.28

For stock option awards granted under the Incentive Plan during the first six months of 2014 and 2013, the fair value was estimated on the date of grant using a Black-Scholes option pricing model and the assumptions noted in the table below. The weighted average grant date fair value per share of the awards granted during the first six months of 2014 and 2013 was $8.11 and $0.90, respectively. The fair value of the stock option awards is amortized to expense over the vesting periods using a straight-line expense attribution method. The following table summarizes the key assumptions used by the Company to value the stock option awards granted during the first six months of 2014 and 2013. The expected life is based on the average of the assumption that all outstanding stock option awards will be exercised at full vesting and the assumption that all outstanding stock option awards will be exercised at the midpoint of the current date (if already vested) or at full vesting (if not yet vested) and the full contractual term. The expected volatility represents the historical volatility on the Company’s publicly traded common stock. The Company has assumed no expected dividend yield, as dividends have never been paid to stock or option holders and will not be paid for the foreseeable future. The weighted average risk-free interest rate is the implied yield currently available on zero-coupon government issues with a remaining term equal to the expected term.

Weighted Average Assumptions for Stock Option Awards Granted to

Employees and Directors under the Incentive Plan

	2014			2013
Expected Life in Years		5.5			4.6
Expected Volatility		87	%		83	%
Expected Dividend Yield		0.0	%		0.0	%
Risk-Free Interest Rate		1.6	%		0.6	%

Employee Stock Purchase Plan

The Company has reserved a total of 1,475 shares of common stock to be purchased under the ESPP, of which 559 shares remain available for purchase at June 30, 2014. Eligible employees may authorize up to 15% of their salary to purchase common stock at the lower of 85% of the beginning or 85% of the ending price during six-month purchase intervals. No more than 3 shares may be purchased by any one employee at the six-month purchase dates and no employee may purchase stock having a fair market value at the commencement date of $25 or more in any one calendar year. The Company issued 28 shares during the first six months of 2014 under the ESPP. Compensation expense for shares purchased under the ESPP related to the purchase discount and the “look-back” option were determined using a Black-Scholes option pricing model.

Note 3 - Collaborative and Other Research and Development Contracts	6 Months Ended
	Jun. 30, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborative Arrangement Disclosure [Text Block]	Note 3 — Collaborative and Other Research and Development Contracts U.S. Department of Health and Human Services (“BARDA/HHS”). In January 2007, the U.S. Department of Health and Human Services (“BARDA/HHS”) awarded the Company a $102,661 contract for the advanced development of peramivir for the treatment of influenza. During 2009, peramivir clinical development shifted to focus on intravenous delivery and the treatment of hospitalized patients. To support this focus, a September 2009 contract modification was awarded to increase funding by $77,191. On February 24, 2011, the Company announced that BARDA/HHS had awarded it a $55,000 contract modification, intended to fund completion of the Phase 3 development of intravenous (“i.v.”) peramivir for the treatment of patients hospitalized with influenza. This contract modification brought the total award from BARDA/HHS to $234,852 and provided funding to support the filing of a new drug application (“NDA”) to seek regulatory approval for i.v. peramivir in the U.S. The contract expired on June 30, 2014 according to its terms. In December 2013, BioCryst submitted a NDA filing for i.v. peramivir to the U.S. Food & Drug Administration (“FDA”) seeking an indication as the first i.v. neuraminidase inhibitor approved in the U.S. for the treatment of acute uncomplicated influenza in adults. On February 24, 2014, the FDA notified the Company its NDA submission had been accepted for review. The FDA is expected to take action on the application by December 23, 2014. National Institute of Allergy and Infectious Diseases (“NIAID/HHS”). In September 2013, NIAID/HHS contracted with the Company for the development of BCX4430 as a treatment for Marburg virus disease. NIAID/HHS, part of the National Institutes of Health, made an initial award of $5.0 million to the Company. The total funding under this contract could be up to $22.0 million, if all contract options are exercised by NIAID/HHS, over a five year period. The goals of this contract are to file initial new drug (“IND”) applications for i.v. and intramuscular (“i.m.”) BCX4430 for the treatment of Marburg virus disease, and to conduct an initial Phase 1 human clinical trial. The aggregate $22.0 million contract and option funding supports the appropriate IND-enabling program and the initial clinical trial. As of June 30, 2014, a total of $9.4 million has been awarded under exercised options within the contract. BCX4430 is the lead compound in the Company’s broad spectrum antiviral (“BSAV”) research program. The contract with NIAID/HHS is a cost-plus-fixed-fee contract. That is, the Company is entitled to receive reimbursement for all costs incurred in accordance with the contract’s provisions that are related to the development of BCX4430 plus a fixed fee, or profit. NIAID/HHS will make periodic assessments of progress, and the continuation of the contract is based on the Company’s performance, the timeliness and quality of deliverables, and other factors. The government has rights under certain contract clauses to terminate this contract. This contract is terminable by the government at any time for breach or without cause. Shionogi & Co., Ltd. (“Shionogi”). In March 2007, the Company entered into an exclusive license agreement with Shionogi to develop and commercialize peramivir in Japan for the treatment of seasonal and potentially life-threatening human influenza. Under the terms of the agreement, Shionogi obtained rights to injectable formulations of peramivir in Japan. The Company developed peramivir under a license from UAB and will owe sublicense payments to them on any future milestone payments and/or royalties received by the Company from Shionogi. In October 2008, the Company and Shionogi amended the license agreement to expand the territory covered by the agreement to include Taiwan and to provide rights for Shionogi to perform a Phase 3 clinical trial in Hong Kong. Shionogi has commercially launched peramivir under the commercial name RAPIACTA ® in Japan. Green Cross Corporation (“Green Cross”). In June 2006, the Company entered into an agreement with Green Cross to develop and commercialize peramivir in Korea. Under the terms of the agreement, Green Cross will be responsible for all development, regulatory, and commercialization costs in Korea. The license provides that the Company will share in profits resulting from the sale of peramivir in Korea, including the sale of peramivir to the Korean government for stockpiling purposes. Furthermore, Green Cross will pay the Company a premium over its cost to supply peramivir for development and any future marketing of peramivir products in Korea. Mundipharma International Holdings Limited (“Mundipharma”). In February 2006, the Company entered into an exclusive, royalty bearing right and license agreement with Mundipharma for the development and commercialization of forodesine, a Purine Nucleoside Phosphorylase (“PNP”) inhibitor, for use in oncology (the “Original Agreement”). Under the terms of the license agreement, as amended, Mundipharma obtained worldwide rights to forodesine. Albert Einstein College of Medicine of Yeshiva University and Industrial Research, Ltd. (“AECOM” and “IRL” respectively). In June 2000, the Company licensed a series of potent inhibitors of PNP from AECOM and IRL, (collectively, the “Licensors”). The lead product candidates from this collaboration are forodesine and ulodesine. The Company has obtained worldwide exclusive rights to develop and ultimately distribute these, or any other, product candidates that might arise from research on these inhibitors. The Company has the option to expand its license agreement with the Licensors to include other inventions in the field made by the investigators or employees of the Licensors. The Company agreed to use commercially reasonable efforts to develop these drugs. In addition, the Company has agreed to pay certain milestone payments for each licensed product (which range in the aggregate from $1,400 to almost $4,000 per indication) for future development of these inhibitors, single digit royalties on net sales of any resulting product made by the Company, and to share approximately one quarter of future payments received from other third-party partners, if any. In addition, the Company has agreed to pay annual license fees, which can range from $150 to $500, that are creditable against actual royalties and other payments due to the Licensors. This agreement may be terminated by the Company at any time by giving 60 days advance notice or in the event of material uncured breach by the Licensors. In May 2010, the Company amended the license agreement through which the Company obtained worldwide exclusive rights to develop and ultimately distribute any product candidates that might arise from research on a series of PNP inhibitors, including forodesine and ulodesine. Under the terms of the amendment, the Licensors agreed to accept a reduction of one-half in the percentage of future payments received from third-party sub licensees of the licensed PNP inhibitors that must be paid to the Licensors. This reduction does not apply to (i) any milestone payments the Company may receive in the future under its license agreement with Mundipharma and (ii) royalties received from its sub licensees in connection with the sale of licensed products, for which the original payment rate will remain in effect. The rate of royalty payments to the Licensors based on net sales of any resulting product made by the Company remains unchanged. In consideration for these modifications in 2010, the Company issued to the Licensors shares of its common stock with an aggregate value of $5,911 and paid the Licensors $90 in cash. Additionally, at the Company’s sole option and subject to certain agreed upon conditions, any future non-royalty payments due to be paid by the Company to the Licensors under the license agreement may be made either in cash, in shares of the Company’s common stock, or in a combination of cash and shares. On November 17, 2011, the Company further amended its agreements with the Licensors whereby the Licensors agreed to accept a reduction of one-half in the percentage of Net Proceeds (as defined in the license agreement) received by the Company under its Amended and Restated Agreement with Mundipharma that will be paid to AECOM/IRL. On June 19, 2012, the Company further amended its agreements with the Licensors whereby the parties clarified the definition of the field with respect to PNP inhibition and the Licensors agreed to grant an exclusive worldwide license of BCX4430 to BioCryst for any antiviral use. At its sole option and subject to certain agreed upon conditions, any future non-royalty payments due to be paid by the Company to the Licensors under the license agreement may be made either in cash, in shares of the Company’s common stock, or in a combination of cash and shares. The University of Alabama at Birmingham (“UAB”). The Company currently has agreements with UAB for influenza neuraminidase and complement inhibitors. Under the terms of these agreements, UAB performed specific research for the Company in return for research payments and license fees. UAB has granted the Company certain rights to any discoveries in these areas resulting from research developed by UAB or jointly developed with the Company. The Company has agreed to pay single digit royalties on sales of any resulting product and to share in future payments received from other third-party partners. The Company has completed the research under the UAB agreements. These two agreements have initial 25-year terms, are automatically renewable for five-year terms throughout the life of the last patent and are terminable by the Company upon three months’ notice and by UAB under certain circumstances. Upon termination both parties shall cease using the other parties’ proprietary and confidential information and materials, the parties shall jointly own joint inventions and UAB shall resume full ownership of all UAB licensed products. There is currently no activity between the Company and UAB on these agreements, but when the Company licenses this technology, such as in the case of the Shionogi and Green Cross agreements, or commercializes products related to these programs, the Company will owe sublicense fees or royalties on amounts it receives.

Note 4 - Royalty Monetization	6 Months Ended
Note 4 - Royalty Monetization	Jun. 30, 2014
Royalty Monetization [Abstract]
Royalty Monetization [Text Block]	Note 4 — Royalty Monetization Overview On March 9, 2011, the Company completed a $30,000 financing transaction to monetize certain future royalty and milestone payments under the Company’s license agreement with Shionogi (the “Shionogi Agreement”), pursuant to which Shionogi licensed from the Company the rights to market RAPIACTA® in Japan and, if approved for commercial sale, Taiwan. The Company received net proceeds of $22,691 from this transaction. As part of the transaction, the Company entered into a purchase and sale agreement dated as of March 9, 2011 with Royalty Sub, whereby the Company transferred to Royalty Sub, among other things, (i) its rights to receive certain royalty and milestone payments from Shionogi arising under the Shionogi Agreement, and (ii) the right to receive payments under a Japanese yen/US dollar foreign currency hedge arrangement (as further described below, the “Currency Hedge Agreement”) put into place by the Company in connection with the transaction. Royalty payments will be paid by Shionogi in Japanese yen and milestone payments will paid in U.S. dollars. The Company’s collaboration with Shionogi was not impacted as a result of this transaction. Non-Recourse Notes Payable On March 9, 2011, Royalty Sub completed a private placement to institutional investors of $30,000 in aggregate principal amount of its PhaRMA Senior Secured 14.0% Notes due 2020 (the “PhaRMA Notes”). The PhaRMA Notes were issued by Royalty Sub under an Indenture, dated as of March 9, 2011 (the “Indenture”), by and between Royalty Sub and U.S. Bank National Association, as Trustee. Principal and interest on the PhaRMA Notes issued are payable from, and are secured by, the rights to royalty and milestone payments under the Shionogi Agreement transferred by the Company to Royalty Sub and payments, if any, made to Royalty Sub under the Currency Hedge Agreement. The PhaRMA Notes bear interest at 14% per annum, payable annually in arrears on September 1st of each year (the “Payment Date”). The Company remains entitled to receive any royalties and milestone payments related to sales of peramivir by Shionogi following repayment by Royalty Sub of the PhaRMA Notes. Royalty Sub’s obligations to pay principal and interest on the PhaRMA Notes are obligations solely of Royalty Sub and are without recourse to any other person, including the Company, except to the extent of the Company’s pledge of its equity interests in Royalty Sub in support of the PhaRMA Notes. The Company may, but is not obligated to, make capital contributions to a capital account that may be used to redeem, or on up to one occasion pay any interest shortfall on, the PhaRMA Notes. In September 2013, Royalty Sub paid $1,844 of interest on the PhaRMA Notes from royalty payments received from RAPIACTA® sales from the preceding four calendar quarters. This payment resulted in an obligation shortfall of approximately $2,356 associated with accrued interest due September 3, 2013. As stipulated under the PhaRMA Notes Indenture, if the amount available for payment on any Payment Date is insufficient to pay all of the interest due on a Payment Date, the shortfall in interest will accrue interest at the interest rate applicable to the PhaRMA Notes compounded annually. Accordingly, commencing in September 2013, the Company began accruing interest at 14% per annum on the interest shortfall of $2,356. In March and June of 2014, Royalty Sub paid additional interest of $446 and $1,882, respectively, bringing the shortfall down to $284 as of June 30, 2014. Under the terms of the Indenture, Royalty Sub’s inability to pay the full amount of interest payable in September 2013 would not constitute an event of default under the PhaRMA Notes unless the shortfall, plus interest thereon, is not satisfied on the next succeeding Payment Date for the PhaRMA Notes, which is September 1, 2014. Based upon information available at June 30, 2014, the Company expects the RAPIACTA® royalty stream from Shionogi, the Company’s partner in Japan, will be insufficient to pay the accrued interest in arrears on the non-recourse PhaRMA Notes by the September 1, 2014 payment date. If the royalty stream is insufficient to pay the interest in arrears, an event of default will occur with respect to the PhaRMA Notes. Accordingly, the Company has classified the PhaRMA Notes and related accrued interest as current liabilities on its balance sheet. If an event of default were to occur under the PhaRMA Notes, the holders of the PhaRMA Notes may pursue acceleration of the PhaRMA Notes, may foreclose on the collateral securing the PhaRMA Notes and the equity interest in Royalty Sub and exercise other remedies available to them under the indenture in respect of the PhaRMA Notes. In such event, the Company may not realize the benefit of future royalty payments that might otherwise accrue to the Company following repayment of the PhaRMA Notes and it might otherwise be adversely affected. Due to the non-recourse nature of the PhaRMA Notes, in the event of any potential acceleration or foreclosure, the Company believes the primary impact to the Company would be the loss of future royalty payments from Shionogi and legal costs associated with retiring the PhaRMA Notes. In addition, the Company may incur costs associated with liquidating the related currency hedge agreement, which would no longer be required in the event of foreclosure or if the PhaRMA Notes cease to be outstanding. As the PhaRMA Notes are the obligation of Royalty Sub, the Company does not currently expect an event of default on the PhaRMA Notes to have a significant impact on the Company’s future results of operations or cash flows. The Indenture does not contain any financial covenants. The Indenture includes customary representations and warranties of Royalty Sub, affirmative and negative covenants of Royalty Sub, Events of Default and related remedies, and provisions regarding the duties of the Trustee, indemnification of the Trustee, and other matters typical for indentures used in structured financings of this type. The PhaRMA Notes are redeemable at the option of Royalty Sub at any time at a redemption price equal to 100% of the outstanding principal balance of the PhaRMA Notes being redeemed, plus accrued and unpaid interest through the redemption date on the PhaRMA Notes being redeemed. Foreign Currency Hedge In connection with the issuance by Royalty Sub of the PhaRMA Notes, the Company entered into a Currency Hedge Agreement to hedge certain risks associated with changes in the value of the Japanese yen relative to the U.S. dollar. Under the Currency Hedge Agreement, the Company has the right to purchase dollars and sell yen at a rate of 100 yen per dollar for which the Company may be required to pay a premium in each year from 2014 through 2020, provided the Currency Hedge Agreement remains in effect. A payment of $1,950 will be required if, on May 18 of the relevant year, the U.S. dollar is worth 100 yen or less as determined in accordance with the Currency Hedge Agreement. The Currency Hedge Agreement does not qualify for hedge accounting treatment; therefore, mark-to-market adjustments are recognized in the Company’s Consolidated Statement of Comprehensive Loss. Cumulative mark-to-market adjustments resulted in a loss of $1,824 and a gain of $1,114 for the three months ended June 30, 2014 and 2013, respectively and a loss of $3,350 and a gain of $3,071 for the six months ended June 30, 2014 and 2013, respectively. The Company is also required to post collateral in connection with the mark-to-market adjustments based on defined thresholds. As of June 30, 2014, $2,700 was posted under the Currency Hedge Agreement. The Company will not be required at any time to post collateral exceeding the maximum premium payments remaining payable under the Currency Hedge Agreement. The maximum amount of hedge collateral the Company would be required to post is $13,650. The Company is required to maintain a foreign currency hedge at 100 yen per dollar under the agreements governing the PhaRMA Notes.

Note 5 - Stockholders' Equity	6 Months Ended
Note 5 - Stockholders' Equity	Jun. 30, 2014
Disclosure Text Block Supplement [Abstract]
Shareholders' Equity and Share-based Payments [Text Block]	Note 5 — Stockholders’ Equity In June 2011, the Company entered into an At Market Issuance Sales Agreement (the “ATM Agreement”) with McNicoll, Lewis & Valak (“MLV”) pursuant to which the Company may issue and sell $70,000 in shares of its common stock at current market prices under a Form S-3 registration statement with MLV acting as the sales agent. Subject to the terms and conditions of the ATM Agreement, MLV will use commercially reasonable efforts to sell the Company’s common stock from time to time, based upon the Company’s instruction, including any price, time or size limits or other customary parameters or conditions the Company may impose. The Company will pay MLV an aggregate commission rate of 2% of the gross proceeds of the sales price per share of any common stock sold under the Agreement depending on the number of shares sold. On June 28, 2011, the Company filed a Registration Statement on Form S-3, which became effective on July 13, 2011, for the issuance and sale of up to $70,000 of equity or other securities. During the six months ended June 30, 2013, the Company sold an aggregate of 2,883 shares of common stock at an average per share price of $1.85 pursuant to the Agreement for net proceeds of $5,218. In August 2013, the Company completed a public offering of 4,600 shares of its common stock at a price of $4.40 per share, which included the underwriters’ over-allotment allocation of an additional 600 shares. Net proceeds were approximately $18,500 after deducting underwriting discounts and offering expenses. In June 2014, the Company completed a public offering of 11,500 shares of its common stock at a price of $10.00 per share, which included the shares purchased pursuant to the underwriters’ option to purchase 1,500 shares. Net proceeds were approximately $106,600 after deducting underwriting discounts and offering expenses.

Accounting Policies, by Policy (Policies)

6 Months Ended

Jun. 30, 2014

Accounting Policies [Abstract]

Description of Company [Policy Text Block]

The Company

Consolidation, Policy [Policy Text Block]

Basis of Presentation

Reclassifications [Policy Text Block]

Reclassifications

Cash and Cash Equivalents, Policy [Policy Text Block]

Cash and Cash Equivalents

Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]

Restricted Cash

Restricted cash as of June 30, 2014 represents cash the Company is required to maintain in an interest bearing certificate of deposit to serve as collateral for a corporate credit card program.

Investment, Policy [Policy Text Block]

Investments

	June 30, 2014
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Corporate debt securities	$	2,278	$	14	$	2	$	—	$	2,294
Commercial paper		8,896		—		1		—		8,897
Total investments	$	11,174	$	14	$	3	$	—	$	11,191

	December 31, 2013
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Obligations of U.S. Government and its agencies	$	4,899	$	1	$	1	$	—	$	4,901
Corporate debt securities		8,528		47		2		1		8,576
Commercial paper		5,994		—		2		—		5,996
Total investments	$	19,421	$	48	$	5	$	1	$	19,473

The following table summarizes the scheduled maturity for the Company’s investments at June 30, 2014 and December 31, 2013.

	2014		2013
Maturing in one year or less	$	10,589	$	16,891
Maturing after one year through two years		602		2,582
Total investments	$	11,191	$	19,473

Receivables, Policy [Policy Text Block]

Receivables

	June 30, 2014
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	236	$	600	$	836
Shionogi & Co. Ltd.		61		—		61
Total receivables	$	297	$	600	$	897

	December 31, 2013
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	90	$	1,573	$	1,663
Shionogi & Co. Ltd.		452		—		452
Total receivables	$	542	$	1,573	$	2,115

Intangible Assets, Finite-Lived, Policy [Policy Text Block]

Patents and Licenses

Accrued Expenses [Policy Text Block]

Accrued Expenses

•

fees paid to Clinical Research Organizations (“CROs”) in connection with preclinical and toxicology studies and clinical trials;

•

fees paid to investigative sites in connection with clinical trials;

•

fees paid to contract manufacturers (“CMOs”) in connection with the production of our raw materials, drug substance and drug products; and

•

professional fees.

Income Tax, Policy [Policy Text Block]

Income Taxes

Accumulated Other Comprehensive Income Loss [Policy Text Block]

Accumulated Other Comprehensive (Loss) Income

Revenue Recognition, Policy [Policy Text Block]

Revenue Recognition

Collaborative and Other Research and Development Arrangements and Royalties

Product Sales

Product sales are recognized net of estimated allowances, discounts, sales returns, chargebacks and rebates.

The Company recorded the following revenues for the three and six months ended June 30, 2014 and 2013:

	Three Months				Six Months
	2014		2013		2014		2013
Royalty revenue	$	125	$	110	$	1,946	$	2,034
Collaborative and other research and development revenues:
U.S. Department of Health and Human Services		1,045		415		2,386		1,749
Shionogi (Japan)		296		296		592		592

Total revenues	$	1,466	$	821	$	4,924	$	4,375

Research and Development Expense, Policy [Policy Text Block]

Research and Development Expenses

Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]

Stock-Based Compensation

Interest Expense and Deferred Financing Costs [Policy Text Block]

Interest Expense and Deferred Financing Costs

Currency Hedge Agreement [Policy Text Block]

Currency Hedge Agreement

Earnings Per Share, Policy [Policy Text Block]

Net Loss Per Share

Use of Estimates, Policy [Policy Text Block]

Use of Estimates

Concentration of Market Risk [Policy Text Block]

Concentration of Market Risk

Concentration Risk, Credit Risk, Policy [Policy Text Block]

Credit Risk

New Accounting Pronouncements, Policy [Policy Text Block]

Recent Accounting Pronouncements

Note 1 - Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2014

Accounting Policies [Abstract]

Available-for-sale Securities [Table Text Block]

	June 30, 2014
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Corporate debt securities	$	2,278	$	14	$	2	$	—	$	2,294
Commercial paper		8,896		—		1		—		8,897
Total investments	$	11,174	$	14	$	3	$	—	$	11,191

	December 31, 2013
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Obligations of U.S. Government and its agencies	$	4,899	$	1	$	1	$	—	$	4,901
Corporate debt securities		8,528		47		2		1		8,576
Commercial paper		5,994		—		2		—		5,996
Total investments	$	19,421	$	48	$	5	$	1	$	19,473

Available for Sale Securities Debt Maturities Fair Value [Table Text Block]

	2014		2013
Maturing in one year or less	$	10,589	$	16,891
Maturing after one year through two years		602		2,582
Total investments	$	11,191	$	19,473

Schedule of Receivables from Collaborations [Table Text Block]

	June 30, 2014
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	236	$	600	$	836
Shionogi & Co. Ltd.		61		—		61
Total receivables	$	297	$	600	$	897

	December 31, 2013
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	90	$	1,573	$	1,663
Shionogi & Co. Ltd.		452		—		452
Total receivables	$	542	$	1,573	$	2,115

Schedule of Revenues from Collaborations [Table Text Block]

	Three Months				Six Months
	2014		2013		2014		2013
Royalty revenue	$	125	$	110	$	1,946	$	2,034
Collaborative and other research and development revenues:
U.S. Department of Health and Human Services		1,045		415		2,386		1,749
Shionogi (Japan)		296		296		592		592

Total revenues	$	1,466	$	821	$	4,924	$	4,375

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Note 2 - Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

	Awards Available			Options Outstanding			Weighted Average Exercise Price
Balance December 31, 2013		1,082			8,986		$	4.99
Plan amendment		3,750			—			—
Restricted stock awards granted		(593	)		—			—
Restricted stock awards cancelled		—			—			—
Stock option awards granted		(505	)		505			10.28
Stock option awards exercised		—			(1,034	)		4.90
Stock option awards cancelled		88			(88	)		8.83
Balance June 30, 2014		3,822			8,369		$	5.28

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2014			2013
Expected Life in Years		5.5			4.6
Expected Volatility		87	%		83	%
Expected Dividend Yield		0.0	%		0.0	%
Risk-Free Interest Rate		1.6	%		0.6	%

Note 1 - Significant Accounting Policies (Details) - Fair Value of the Company’s Investments by Type - USD ($) $ in Thousands	Jun. 30, 2014	Dec. 31, 2013
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,278	$ 8,528
Accrued Interest	14	47
Gross Unrealized Gains	2	2
Gross Unrealized Losses		1
Estimated Fair Value	2,294	8,576
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,896	5,994
Accrued Interest	0	0
Gross Unrealized Gains	1	2
Gross Unrealized Losses	0	0
Estimated Fair Value	8,897	5,996
US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		4,899
Accrued Interest		1
Gross Unrealized Gains		1
Gross Unrealized Losses		0
Estimated Fair Value		4,901
Amortized Cost	11,174	19,421
Accrued Interest	14	48
Gross Unrealized Gains	3	5
Gross Unrealized Losses		1
Estimated Fair Value	$ 11,191	$ 19,473

Note 1 - Significant Accounting Policies (Details) - Scheduled Maturity for the Company’s Investments - USD ($) $ in Thousands	Jun. 30, 2014	Dec. 31, 2013
Scheduled Maturity for the Company’s Investments [Abstract]
Maturing in one year or less	$ 10,589	$ 16,891
Maturing after one year through two years	602	2,582
Total investments	$ 11,191	$ 19,473

Note 1 - Significant Accounting Policies (Details) - Summary of Receivables - USD ($) $ in Thousands	Jun. 30, 2014	Dec. 31, 2013
U.S. Department of Health and Human Services [Member] \| Billed Revenues [Member]
Note 1 - Significant Accounting Policies (Details) - Summary of Receivables [Line Items]
Receivables	$ 236	$ 90
U.S. Department of Health and Human Services [Member] \| Unbilled Revenues [Member]
Note 1 - Significant Accounting Policies (Details) - Summary of Receivables [Line Items]
Receivables	600	1,573
U.S. Department of Health and Human Services [Member]
Note 1 - Significant Accounting Policies (Details) - Summary of Receivables [Line Items]
Receivables	836	1,663
Shionogi & Co. Ltd. [Member] \| Billed Revenues [Member]
Note 1 - Significant Accounting Policies (Details) - Summary of Receivables [Line Items]
Receivables	61	452
Shionogi & Co. Ltd. [Member]
Note 1 - Significant Accounting Policies (Details) - Summary of Receivables [Line Items]
Receivables	$ 61	$ 452

Note 1 - Significant Accounting Policies (Details) - Summary of Revenues - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
U.S. Department of Health and Human Services [Member]
Collaborative and other research and development revenues:
Collaborative and other research and development revenues	$ 1,045	$ 415	$ 2,386	$ 1,749
Shionogi & Co. Ltd. [Member]
Collaborative and other research and development revenues:
Collaborative and other research and development revenues	$ 296	$ 296	$ 592	$ 592

Note 2 - Stock-Based Compensation (Details) - Employee Stock Option [Member] - Incentive Plan [Member]	6 Months Ended
	Jun. 30, 2014
Minimum [Member]
Note 2 - Stock-Based Compensation (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	5 years
Maximum [Member]
Note 2 - Stock-Based Compensation (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	10 years

Note 2 - Stock-Based Compensation (Details) - Summary of Related Activity under the Incentive Plan shares in Thousands	6 Months Ended
	Jun. 30, 2014 $ / shares shares
Summary of Related Activity under the Incentive Plan [Abstract]
Awards Available	1,082
Options Outstanding	8,986
Weighted Average Exercise Price (in Dollars per share) \| $ / shares	$ 4.99
Plan amendment	3,750
Restricted stock awards granted	(593)
Stock option awards granted	(505)
Stock option awards granted	505
Stock option awards granted (in Dollars per share) \| $ / shares	$ 10.28
Stock option awards exercised	(1,034)
Stock option awards exercised (in Dollars per share) \| $ / shares	$ 4.90
Stock option awards cancelled	88
Stock option awards cancelled	(88)
Stock option awards cancelled (in Dollars per share) \| $ / shares	$ 8.83
Awards Available	3,822
Options Outstanding	8,369
Weighted Average Exercise Price (in Dollars per share) \| $ / shares	$ 5.28

Note 2 - Stock-Based Compensation (Details) - Weighted Average Assumptions for Stock Option Awards Granted to Employees and Directors under the Incentive Plan	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Weighted Average Assumptions for Stock Option Awards Granted to Employees and Directors under the Incentive Plan [Abstract]
Expected Life in Years	5 years 6 months	4 years 219 days
Expected Volatility	87.00%	83.00%
Expected Dividend Yield	0.00%	0.00%
Risk-Free Interest Rate	1.60%	0.60%

Note 3 - Collaborative and Other Research and Development Contracts (Details) - AECOM and IRL [Member] - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	May 31, 2010	Jun. 30, 2014
Note 3 - Collaborative and Other Research and Development Contracts (Details) [Line Items]
Milestone Payment Minimum		$ 1,400
Milestone Payment Maximum		4,000
Annual License Fee Minimum		150
Annual License Fee Maximum		$ 500
Advance Notice Period for Termination of Agreement		60 days
Stock Issued During Period Value for Modification of License Agreement	$ 5,911
Payments for Modification of License Agreement	$ 90

Note 4 - Royalty Monetization (Details) - Currency Hedge Agreement [Member] $ in Thousands			3 Months Ended		6 Months Ended
	May 18, 2014 JPY (¥)	May 18, 2014 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2013 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2014 JPY (¥)	Jun. 30, 2013 USD ($)	Jun. 30, 2014 JPY (¥)
Scenario, U.S. Dollar worth 100 Yen or Less [Member]
Note 4 - Royalty Monetization (Details) [Line Items]
Payments for (Proceeds from) Hedge, Investing Activities		$ 1,950
Yen Rate Per Dollar (in Yen) \| ¥						¥ 100
Minimum Currency Value Required for Payment of Premium on Specified Date (in Yen) \| ¥	¥ 100
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments			$ (1,824)	$ 1,114	$ (3,350)		$ 3,071
Currency Hedge Agreement Amount			2,700		2,700
Maximum Amount of Collateral Required to Post			$ 13,650		$ 13,650
Required Foreign Currency Hedge, Per Dollar (in Yen) \| ¥								¥ 100

Note 5 - Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended			6 Months Ended
	Jun. 30, 2014	Aug. 31, 2013	Jun. 30, 2011	Jun. 30, 2013	Dec. 31, 2013
Common Stock [Member]
Note 5 - Stockholders' Equity (Details) [Line Items]
Stock Issued During Period, Shares, New Issues (in Shares)				2,883
Sale of Stock, Average Price Per Share (in Dollars per share)				$ 1.85
Common Stock, Value, Issued	$ 717		$ 70,000		$ 591
Retail Land Sale Receivables, Weighted Average Interest Rate			2.00%
Common Stock Maximum Value Authorized For Issuance			$ 70,000
Stock Issued During Period, Shares, New Issues (in Shares)		4,600
Proceeds from Issuance or Sale of Equity	$ 106,600	$ 18,500		$ 5,218
Share Price (in Dollars per share)	$ 10.00	$ 4.40
Stock Issued During Period, Shares for Over Allotment Option Exercised by Underwriter (in Shares)	1,500	600
Stock Issued During Period, Value, New Issues	$ 11,500

Label	Element	Value
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Payments	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPayments	$ 0
Investments and Cash	us-gaap_InvestmentsAndCash	132,860,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax	0
EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearFour	bcrx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearFour	$ 2,153,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	5,038,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	978,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	5,123,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	852,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	$ 8.11
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	$ 0.90
Amortization of debt issuance costs	us-gaap_AmortizationOfFinancingCosts	$ 110,000
Amortization of debt issuance costs	us-gaap_AmortizationOfFinancingCosts	110,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions	0
ReclassificationAdjustmentsFromResearchAndDevelopmentExpenseToGeneralAndAdministrativeExpense	bcrx_ReclassificationAdjustmentsFromResearchAndDevelopmentExpenseToGeneralAndAdministrativeExpense	201,000
ReclassificationAdjustmentsFromResearchAndDevelopmentExpenseToGeneralAndAdministrativeExpense	bcrx_ReclassificationAdjustmentsFromResearchAndDevelopmentExpenseToGeneralAndAdministrativeExpense	397,000
AccruedResearchAndDevelopmentExpenses	bcrx_AccruedResearchAndDevelopmentExpenses	1,392,000
AccruedResearchAndDevelopmentExpenses	bcrx_AccruedResearchAndDevelopmentExpenses	2,210,000
EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearThree	bcrx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearThree	$ 2,619,000
NumberOfStockBasedCompensationPlans	bcrx_NumberOfStockBasedCompensationPlans	2
Allocated Share-based Compensation Expense	us-gaap_AllocatedShareBasedCompensationExpense	$ 5,129,000
Allocated Share-based Compensation Expense	us-gaap_AllocatedShareBasedCompensationExpense	2,521,000
EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearTwo	bcrx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearTwo	3,688,000
EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearFive	bcrx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearFive	174,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized	11,182,000
EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedForRemainderOfFiscalYear	bcrx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedForRemainderOfFiscalYear	2,548,000
Total revenues	us-gaap_Revenues	1,466,000
Total revenues	us-gaap_Revenues	821,000
Total revenues	us-gaap_Revenues	4,924,000
Total revenues	us-gaap_Revenues	4,375,000
Currency Hedge Agreement [Member]
CashCollateralMarginFunds	bcrx_CashCollateralMarginFunds	2,700,000
CashCollateralMarginFunds	bcrx_CashCollateralMarginFunds	$ 0
UAB [Member]
NumberOfAgreements	bcrx_NumberOfAgreements	2
PeriodOfAgreement	bcrx_PeriodOfAgreement	25 years
RenewablePeriodOfAgreement	bcrx_RenewablePeriodOfAgreement	5 years
US Department Of Health And Human Services [Member]
CollaborativeAgreementAdjustedContractValue	bcrx_CollaborativeAgreementAdjustedContractValue	$ 234,852,000
CollaborativeAgreementAdditionalContractValue	bcrx_CollaborativeAgreementAdditionalContractValue	77,191,000
CollaborativeAgreementAdditionalContractValue	bcrx_CollaborativeAgreementAdditionalContractValue	55,000,000
CollaborativeAgreementContractValue	bcrx_CollaborativeAgreementContractValue	102,661,000
National Institute Of Allergy And Infectious Diseases [Member]
ProceedsFromAwardsForResearchAndDevelopmentContracts	bcrx_ProceedsFromAwardsForResearchAndDevelopmentContracts	$ 5,000,000
CollaborativeAgreementPeriodOfContract	bcrx_CollaborativeAgreementPeriodOfContract	5 years
ExpectedReceivableFromAwardsForResearchAndDevelopmentContracts	bcrx_ExpectedReceivableFromAwardsForResearchAndDevelopmentContracts	$ 22,000,000
CollaborationAgreementAdditionalPaymentsReceived	bcrx_CollaborationAgreementAdditionalPaymentsReceived	$ 9,400,000
Maximum [Member]
AverageMaturityForPortfolioInvestments	bcrx_AverageMaturityForPortfolioInvestments	24 months
MaturityPeriodOfHighQualityMarketableSecurities	bcrx_MaturityPeriodOfHighQualityMarketableSecurities	3 years
MaturityPeriodOfShortTermInvestment	bcrx_MaturityPeriodOfShortTermInvestment	12 months
MaturityOfInvestments	bcrx_MaturityOfInvestments	3 months
AverageMaturityPeriodOfHighQualityMarketableSecurities	bcrx_AverageMaturityPeriodOfHighQualityMarketableSecurities	18 months
Minimum [Member]
MaturityPeriodOfShortTermInvestment	bcrx_MaturityPeriodOfShortTermInvestment	3 months
LongTermInvestmentMaturityMinimum	bcrx_LongTermInvestmentMaturityMinimum	12 months
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized	1,475,000
EmployeeStockPurchasePlanPeriodToPurchaseCommonStock	bcrx_EmployeeStockPurchasePlanPeriodToPurchaseCommonStock	6 months
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant	559,000
PercentageOfCommonStockSharesEnding	bcrx_PercentageOfCommonStockSharesEnding	85.00%
ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployeeAmount	bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployeeAmount	25,000
Allocated Share-based Compensation Expense	us-gaap_AllocatedShareBasedCompensationExpense	$ 109,000
Allocated Share-based Compensation Expense	us-gaap_AllocatedShareBasedCompensationExpense	$ 42,000
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate	15.00%
Stock Issued During Period, Shares, Employee Stock Purchase Plans	us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans	28,000
PercentageOfCommonStockSharesBeginning	bcrx_PercentageOfCommonStockSharesBeginning	85.00%
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee	3,000
Incentive Plan [Member]
Allocated Share-based Compensation Expense	us-gaap_AllocatedShareBasedCompensationExpense	$ 5,020,000
Allocated Share-based Compensation Expense	us-gaap_AllocatedShareBasedCompensationExpense	2,479,000
Pha RMA Notes [Member]
DeductionInInterest	bcrx_DeductionInInterest	2,356,000
DeductionInInterest	bcrx_DeductionInInterest	$ 284,000
Debt Instrument, Interest Rate, Stated Percentage	us-gaap_DebtInstrumentInterestRateStatedPercentage	14.00%
PrivatePlacementOfSeniorSecuredNotes	bcrx_PrivatePlacementOfSeniorSecuredNotes	$ 30,000,000
PercentageOfPrincipalAmountRedemptionPrice	bcrx_PercentageOfPrincipalAmountRedemptionPrice	100.00%
Debt Instrument, Periodic Payment, Interest	us-gaap_DebtInstrumentPeriodicPaymentInterest	$ 1,844,000
Debt Instrument, Periodic Payment, Interest	us-gaap_DebtInstrumentPeriodicPaymentInterest	446,000
Debt Instrument, Periodic Payment, Interest	us-gaap_DebtInstrumentPeriodicPaymentInterest	1,882,000
JPR Royalty Sub LLC [Member]
RevenueRecognitionRoyaltyAndMilestoneRevenueRecognizedNet	bcrx_RevenueRecognitionRoyaltyAndMilestoneRevenueRecognizedNet	22,691,000
RevenueRecognitionRoyaltyAndMilestoneRevenueRecognized	bcrx_RevenueRecognitionRoyaltyAndMilestoneRevenueRecognized	30,000,000
Billed Revenues [Member]
Receivables	us-gaap_ReceivablesNetCurrent	297,000
Receivables	us-gaap_ReceivablesNetCurrent	542,000
Unbilled Revenues [Member]
Receivables	us-gaap_ReceivablesNetCurrent	600,000
Receivables	us-gaap_ReceivablesNetCurrent	$ 1,573,000
Stock Options And Restricted Stock [Member] \| Incentive Plan [Member] \| Retention Grants Made In January 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1	2 years
ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentage	bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentage	50.00%
Employee Stock Option [Member] \| Incentive Plan [Member] \| Performance Based Grants Made In August 2013 Unvested Portion [Member]
Allocated Share-based Compensation Expense	us-gaap_AllocatedShareBasedCompensationExpense	$ 0
Employee Stock Option [Member] \| Incentive Plan [Member] \| Performance Based Grants Made In August 2013 [Member]
ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentage	bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentage	25.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	1,032,000
ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardsUnvestedPercentage	bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardsUnvestedPercentage	75.00%
Employee Stock Option [Member] \| Incentive Plan [Member] \| Grants Commencing March 12011 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1	4 years
ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentage	bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentage	25.00%
Employee Stock Option [Member] \| Incentive Plan [Member] \| Non-employee Directors [Member]
ShareBasedCompensationArrangementByShareBasedPaymentAwardFirstVestingPeriodAfterGrantDate	bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardFirstVestingPeriodAfterGrantDate	1 year