Employee 401(k) Plan - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Compensation And Retirement Disclosure [Abstract]
Matching contributions plan	$ 313	$ 418	$ 391

Defined contribution plan employer matching contribution amount.

No definition available.

Name:	bcrx_DefinedContributionPlanEmployerMatchingContributionAmount
Namespace Prefix:	bcrx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration