Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 29, 2018
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Trading Symbol	RGEN
Entity Registrant Name	REPLIGEN CORP
Entity Central Index Key	0000730272
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Emerging growth company	false
Smaller reporting company	false
Entity Common Stock, Shares Outstanding		43,859,319