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.