Commitments And Contingent Liabilities (Details) $ in Millions	Dec. 31, 2023 USD ($)
Other Assets
Unfunded commitments related to investments in private funds, low-income housing tax credit investments, and equity method investees.	$ 5

The amount of unfunded commitments related to investments for which the entity is obligated, including investments in private funds, low-income housing tax credit investments and equity method investments.

No definition available.

Name:	rli_InvestmentsUnfundedCommitments
Namespace Prefix:	rli_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant