Name:	rli_MinimumPercentageOfReinsuranceRecoverablesFromEntitiesWithFinancialStrengthRatingsOfAOrBetter
Namespace Prefix:	rli_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

A valuation allowance for the amount deemed uncollectible of an insurance receivable related to a policy by which an insurer indemnifies itself of some or all of the risk associated with another insurance policy. Includes the carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross premiums receivable to net realizable value.

No definition available.

Name:	rli_PremiumsAndReinsuranceBalancesReceivableAllowances
Namespace Prefix:	rli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The carrying amount due to the entity beyond one year from the balance sheet date from (a) agents and insureds, (b) uncollected premiums and (c) others, net of the allowance for doubtful accounts. Also includes receivables due after one year from the balance sheet date from reinsurers for ceded claims paid.

No definition available.

Name:	rli_PremiumsAndReinsuranceBalancesReceivableBeyondOneYear
Namespace Prefix:	rli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The unexpired portion of premiums ceded on policies in force as of the balance sheet date, and the known and estimated amount recoverable as of the balance sheet date from reinsurers for claims paid or incurred by the ceding insurer and associated claims settlement expenses, including estimated amounts for claims incurred but not reported, and policy benefits, net of any related valuation allowance.

No definition available.

Name:	rli_PrepaidReinsurancePremiumsAndRecoverablesOnLossesAndSettlementExpenses
Namespace Prefix:	rli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the threshold period beyond which receivables due under reinsurance arrangements are included in the allowance for uncollectible amounts, unless separately disclosed.

No definition available.

Name:	rli_ReinsuranceReceivablesThresholdPeriod
Namespace Prefix:	rli_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Represents the number of top reinsurers for which the entity discloses individual reinsurance balances recoverable.

No definition available.

Name:	rli_ReinsuranceRecoverableNumberOfTopReinsurers
Namespace Prefix:	rli_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

A valuation allowance for the amount deemed uncollectible of the known and estimated amount recoverable as of the balance sheet date from reinsurers for unpaid claims incurred by the ceding insurer and associated claims settlement expenses, including estimated amounts for claims incurred but not reported, and policy benefits.

No definition available.

Name:	rli_ReinsuranceRecoverablesUnpaidLossesAllowances
Namespace Prefix:	rli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the reinsurance balances recoverable from individual reinsurer expressed as a percentage of shareholders' equity, used as a threshold for disclosure.

No definition available.

Name:	rli_ThresholdReinsuranceRecoverableFromIndividualReinsurerAsPercentageOfShareholdersEquity
Namespace Prefix:	rli_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Details

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

The known and estimated amount recoverable as of the balance sheet date from reinsurers for claims paid or incurred by the ceding insurer and associated claims settlement expenses, including estimated amounts for claims incurred but not reported, and policy benefits, net of any related valuation allowance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.(a),6)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 03

-Paragraph 6

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 113

-Paragraph 14, 16, 27, 113

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 20

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387