| Document and Entity Information | Jul. 29, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jul. 29, 2020 |
| Entity Registrant Name | JAMES RIVER GROUP HOLDINGS, LTD. |
| Entity Central Index Key | 0001620459 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | D0 |
| Entity File Number | 001-36777 |
| Entity Tax Identification Number | 98-0585280 |
| Entity Address, Address Line One | 90 Pitts Bay Road |
| Entity Address, Address Line Two | 2nd Floor |
| Entity Address, Address Line Three | Wellesley House |
| Entity Address, City or Town | Pembroke |
| Entity Address, Postal Zip Code | HM08 |
| Entity Address, Country | BM |
| City Area Code | 441 |
| Local Phone Number | 278-4580 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Shares, par value $0.0002 per share |
| Trading Symbol | JRVR |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
