| Cover - USD ($) | 12 Months Ended | | |
| Dec. 31, 2021 | Feb. 25, 2022 | Jun. 30, 2021 |
| Cover [Abstract] | | | |
| Document Type | 10-K/A | | |
| Document Annual Report | true | | |
| Document Period End Date | Dec. 31,
2021 | | |
| Current Fiscal Year End Date | --12-31 | | |
| Document Transition Report | false | | |
| Entity File Number | 001-36777 | | |
| Entity Registrant Name | JAMES RIVER GROUP HOLDINGS, LTD. | | |
| Entity Incorporation, State or Country Code | D0 | | |
| Entity Well-known Seasoned Issuer | Yes | | |
| Entity Common Stock, Shares Outstanding | | 37,448,314 | |
| Amendment Flag | true | | |
| Document Fiscal Period Focus | FY | | |
| Document Fiscal Year Focus | 2021 | | |
| Entity Tax Identification Number | 98-0585280 | | |
| Entity Address, Address Line Three | Wellesley House | | |
| Entity Address, Address Line Two | 2nd Floor | | |
| Entity Address, Address Line One | 90 Pitts Bay Road | | |
| 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 | | |
| Title of 12(b) Security | Common Shares, par value $0.0002 per share | | |
| Trading Symbol | JRVR | | |
| Security Exchange Name | NASDAQ | | |
| Entity Interactive Data Current | Yes | | |
| Entity Voluntary Filers | No | | |
| Entity Current Reporting Status | Yes | | |
| Entity Filer Category | Large Accelerated Filer | | |
| Entity Small Business | false | | |
| Entity Emerging Growth Company | false | | |
| Entity Shell Company | false | | |
| ICFR Auditor Attestation Flag | true | | |
| Entity Public Float | | | $ 1,362,783,768 |
| Entity Central Index Key | 0001620459 | | |
| Amendment Description | James River Group Holdings, Ltd. (the “Company”, “our”, “us” or “we”) is filing this Amendment No. 1 on Form 10-K/A (this “Form 10-K/A”) to its Annual Report on Form 10-K for the fiscal year ended December 31, 2021 (the “Original Form 10-K”) that was filed with the Securities and Exchange Commission (“SEC”) on March 1, 2022 for the sole purpose of including the information required by Part III of Form 10-K. This Part III information was previously omitted from the Original Form 10-K in reliance on General Instruction G(3) to Form 10-K, which permits the information in Part III to be incorporated in Form 10-K by reference to the Company’s definitive proxy statement if such statement is filed no later than 120 days after the end of our fiscal year. The Company does not intend to file its definitive proxy statement for its 2022 Annual General Meeting of Shareholders within 120 days of December 31, 2021, as it intends to delay its 2022 Annual General Meeting of Shareholders to a later date within the 2022 fiscal year.As required by Rule 12b-15, in connection with this Form 10-K/A, the Company’s Principal Executive Officer and Principal Financial Officer are providing Rule 13a-14(a) certifications included herein.Except as explicitly set forth herein, this Form 10-K/A does not purport to modify or update the disclosures in, or exhibits to, the Original Form 10-K or to update the Original Form 10-K to reflect events occurring after the date of such filing. | | |
