The fair value at grant date for nonvested equity-based awards issued during the period on restricted stock units.

No definition available.

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Represents the participant's age and period of service to be considered retirement eligible under the plan.

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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- Definition

Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- 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.

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No definition available.

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Number of shares authorized for issuance under share-based payment arrangement.

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- Definition

Net number of share options (or share units) granted during the period.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

+ References

No definition available.

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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Stock Based Compensation - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended	60 Months Ended	65 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	May 06, 2015	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted (in shares)			275,977	324,525
Award vesting period			5 years
Term of options			8 years
Age and period of service of the participant to be eligible for retirement			75 years
Weighted average exercise price			$ 93.39	$ 81.27
Weighted-average fair value			$ 13.33	$ 13.47
Stock-based compensation expenses	$ 1,300,000	$ 1,200,000	$ 2,800,000	$ 3,600,000
Income tax benefit from stock-based compensation	300,000	200,000	600,000	700,000
Unrecognized stock-based compensation expense	5,600,000		$ 5,600,000				$ 5,600,000
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period			3 years
Age and period of service of the participant to be eligible for retirement			75 years
Stock-based compensation expenses	200,000	300,000	$ 500,000	600,000
Unrecognized stock-based compensation expense	$ 1,600,000		$ 1,600,000				$ 1,600,000
RSUs Granted							58,420
RSUs Outstanding	41,826		41,826				41,826
Restricted Stock Units (RSUs) \| Outside director
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period			1 year
Stock-based compensation expenses	$ 100,000	$ 100,000	$ 200,000	$ 500,000
RSUs Granted							20,445
RSUs Outstanding	5,375		5,375				5,375
Grant date fair value of RSUs			$ 50,000		$ 50,000
RLI Corp. Long-Term Incentive Plan (2010 LTIP)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for grant						4,000,000
Options granted (in shares)						2,878,000
RLI Corp. Long-Term Incentive Plan (2015 LTIP)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for grant	4,000,000		4,000,000				4,000,000
Options granted (in shares)							2,576,867