Represents interest reserve established as part of the royalty monetization.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents maximum amount of collateral required to post.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Represents the percentage of carrying amount in excess of fair value.

+ References

No definition available.

+ Details

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Namespace Prefix:	bcrx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents private placement of senior secured notes.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The Company is required to maintain a foreign currency hedge per dollar under the agreements governing the PhaRMA Notes.

+ References

No definition available.

+ Details

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Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents transaction costs associated with royalty monetization.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual rate at which a foreign currency can be purchased or sold.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeForwardExchangeRate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of increase in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of decrease in the fair value of derivatives recognized in the income statement.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair value portion of notes payable.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash outflow or inflow for a financial contract that meets the hedge criteria as either a cash flow hedge, fair value hedge, or hedge of a net investment in a foreign operation.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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-SubTopic 10
-Section S99
-Paragraph 3
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-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow from amounts received from issuance of long-term debt that is wholly or partially secured by collateral. Excludes proceeds from tax exempt secured debt.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-SubTopic 10
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Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
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Period Type:

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Note 3 - Royalty Monetization (Details Textual) $ in Thousands			12 Months Ended
	May 18, 2016 USD ($)	Mar. 09, 2011 USD ($)	Dec. 31, 2018 USD ($) ¥ / $	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Currency Hedge Agreement [Member]
Collateral Already Posted, Aggregate Fair Value			$ 0	$ 0
Foreign Exchange Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivative, Loss on Derivative			1,049	1,787	$ 1,654
Derivative, Gain on Derivative			$ 941	966	$ 811
PhaRMA Notes Member] \| Currency Hedge Agreement [Member]
Payments for (Proceeds from) Hedge, Investing Activities, Total	$ 1,950
Required Foreign Currency Hedge Per Dollar	100
PhaRMA Notes Member] \| Japan, Yen \| Currency Hedge Agreement [Member]
Derivative, Forward Exchange Rate \| ¥ / $			100
JPR Royalty Sub LLC [Member] \| PhaRMA Notes Member]
Private Placement of Senior Secured Notes		$ 30,000
Debt Instrument, Interest Rate, Stated Percentage		14.00%
Percentage of Carrying Amount in Excess of Fair Value			50.00%
JPR Royalty Sub LLC [Member] \| PhaRMA Notes Member] \| Currency Hedge Agreement [Member]
Collateral Already Posted, Aggregate Fair Value			$ 0	$ 0
Maximum Amount of Collateral Required to Post			3,900
JPR Royalty Sub LLC [Member] \| PhaRMA Notes Member] \| Fair Value, Inputs, Level 2 [Member]
Notes Payable, Fair Value Disclosure			$ 30,000
JPR Royalty Sub LLC [Member] \| Royalty Monetization [Member]
Debt Instrument, Face Amount		$ 30,000
Proceeds from Issuance of Secured Debt		22,691
Transaction Costs		4,309
Interest Reserve		$ 3,000