Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Jan. 31, 2021	Jun. 30, 2020
Document Information [Line Items]
Entity Central Index Key	0000882796
Entity Registrant Name	BIOCRYST PHARMACEUTICALS INC
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	000-23186
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	62-1413174
Entity Address, Address Line One	4505 Emperor Blvd., Suite 200
Entity Address, City or Town	Durham
Entity Address, State or Province	NC
Entity Address, Postal Zip Code	27703
City Area Code	919
Local Phone Number	859-1302
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	BCRX
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 832,869,919
Entity Common Stock, Shares Outstanding		177,182,751