Represents the number of insurance companies through which the entity conducts operations.

No definition available.

Name:	rli_NumberOfInsuranceCompaniesThroughWhichOperationsConducted
Namespace Prefix:	rli_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Face amount or stated value per share of common stock.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

+ Details

Name:	us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of states the entity operates in as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ProductInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 4.C)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-4

+ Details

Name:	us-gaap_StockholdersEquityNoteStockSplitConversionRatio1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=rli_RLIInsuranceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=rli_HawleyInsuranceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=rli_ContractorsBondingAndInsuranceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Summary of Significant Accounting Policies - Description of Business (Details)		12 Months Ended
	Jan. 15, 2025 $ / shares	Dec. 31, 2024 company state $ / shares	Dec. 31, 2023 $ / shares
DESCRIPTION OF BUSINESS
Number of insurance companies through which the entity conducts operations \| company		3
Common stock split ratio	2
Common stock, par value (in dollars per share) \| $ / shares	$ 0.01	$ 0.01	$ 0.01
RLI Ins.
DESCRIPTION OF BUSINESS
Number of states in which entity operates		50
Mt. Hawley Insurance Company
DESCRIPTION OF BUSINESS
Number of states in which entity operates		50
Contractors Bonding and Insurance Company
DESCRIPTION OF BUSINESS
Number of states in which entity operates		50