Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 18, 2020	Jun. 28, 2019
Cover [Abstract]
Amendment Flag	false
Document Type	10-K
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0000730272
Current Fiscal Year End Date	--12-31
Document Period End Date	Dec. 31, 2019
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity File Number	000-14656
Entity Registrant Name	REPLIGEN CORP
Entity Filer Category	Large Accelerated Filer
Trading Symbol	RGEN
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-2729386
Entity Address, Address Line One	41 Seyon Street, Bldg. 1, Suite 100
Entity Address, City or Town	Waltham
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02453
City Area Code	781
Entity Shell Company	false
Smaller reporting company	false
Emerging growth company	false
Local Phone Number	250-0111
Document Annual Report	true
Document Transition Report	false
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 3,599,784,849
Entity Common Stock, Shares Outstanding		52,083,563