Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Oct. 27, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
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 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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Central Index Key	0001620459
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		30,610,153
Amendment Flag	false
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2020