Document and Entity Information	6 Months Ended
	Sep. 30, 2011	Oct. 31, 2011
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2011
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q2
Trading Symbol	RGEN
Entity Registrant Name	REPLIGEN CORP
Entity Central Index Key	0000730272
Current Fiscal Year End Date	--03-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		30,714,757