| Document and Entity Information | Jan. 27, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | REPLIGEN CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0000730272 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Jan. 27, 2021 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 000-14656 |
| Entity Tax Identification Number | 04-2729386 |
| Entity Address, Address Line One | 41 Seyon Street |
| Entity Address, Address Line Two | Bldg. 1 |
| Entity Address, Address Line Three | Suite 100 |
| Entity Address, City or Town | Waltham |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02453 |
| City Area Code | (781) |
| Local Phone Number | 250-0111 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | RGEN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
