Condensed Consolidated Statements of Cash Flows (Unaudited) (Parentheticals) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021
Statement of Cash Flows [Abstract]
Cash provided by operating activities excluding reduction in collateral funds	$ 139.2	$ 43.4

Net Cash Provided by (Used in) Operating Activities Excluding Change in Collateral Funds

No definition available.

Name:	jrvr_NetCashProvidedByUsedInOperatingActivitiesExcludingChangeInCollateralFunds
Namespace Prefix:	jrvr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration