EMPLOYEE BENEFITS (Details 2) - 10K (USD $)	1 Months Ended			12 Months Ended			0 Months Ended						3 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 22, 2014	Nov. 13, 2014	Dec. 20, 2013	Nov. 14, 2013	Dec. 20, 2012	Nov. 14, 2012	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2005
Stock options and stock plans
Dividend paid (in dollars per share)				$ 3.71	$ 2.17	$ 3.13
Nonqualified options as percentage of options outstanding				99.00%
Weighted Number of Options Outstanding
Outstanding options at the beginning of the period (in shares)				2,595,084	2,945,204	2,561,732							2,595,084	2,945,204
Options granted (in shares)	369,500	472,700	437,800	512,000	632,700	669,800
Special dividend (in shares)				415	272	2,172
Options exercised (in shares)				(214,042)	(935,692)	(282,260)
Options canceled/forfeited (in shares)				(740)	(47,400)	(6,240)
Outstanding options at the end of the period (in shares)				2,892,717	2,595,084	2,945,204
Exercisable options at the end of the period (in shares)				1,238,257	934,544	1,362,184
Weighted Average Exercise Price
Outstanding options at the beginning of the period (in dollars per share)				$ 26.04	$ 22.22	$ 21.62							$ 26.04	$ 22.22
Options granted (in dollars per share)				$ 40.46	$ 35.67	$ 31.71
Special dividend (in dollars per share)				$ 16.72	$ 16.38	$ 15.39
Options exercised (in dollars per share)				$ 18.93	$ 17.40	$ 19.03
Options canceled/forfeited (in dollars per share)				$ 13.51	$ 24.86	$ 20.42
Outstanding options at the end of the period (in dollars per share)				$ 26.65	$ 26.04	$ 22.22
Exercisable options at the end of the period (in dollars per share)				$ 20.02	$ 20.36	$ 18.29
Weighted Average Remaining Contractual Life
Weighted-average remaining contractual term of options outstanding				5 years 2 months 5 days	5 years 6 months 22 days	5 years 5 months 5 days
Weighted-average remaining contractual term of exercisable options				3 years 11 months 9 days	4 years 3 months 11 days	4 years 3 months 7 days
Aggregate Intrinsic Value
Options exercised (in dollars)				$ 6,164,000	$ 22,422,000	$ 4,712,000
Outstanding options at the end of the period (in dollars)				65,809,000	58,790,000	29,865,000
Exercisable options at the end of the period (in dollars)				36,385,000	26,474,000	19,135,000
Weighted-average fair value of options granted (in dollars per share)	$ 7.71	$ 6.47	$ 6.54	$ 7.89	$ 6.88	$ 6.55
Stock-based compensation expenses (in dollars)				3,900,000	3,800,000	3,600,000
Income tax benefit from stock-based compensation (in dollars)				1,400,000	1,300,000	1,300,000
Unrecognized stock-based compensation expense (in dollars)				4,800,000	4,500,000	4,300,000
Weighted average grant date assumptions and weighted average fair value
Weighted-average fair value of grants (in dollars per share)	$ 7.71	$ 6.47	$ 6.54	$ 7.89	$ 6.88	$ 6.55
Risk-free interest rates (as a percent)				1.70%	0.87%	0.90%
Dividend yield (as a percent)				1.94%	2.00%	1.93%
Expected volatility (as a percent)				23.17%	25.40%	25.62%
Expected option life				5 years 2 months 9 days	5 years 3 months 4 days	5 years 5 months 5 days
Period for which annualized dividends is considered to calculate dividend yield				5 years
Special Cash Dividends Member
Stock options and stock plans
Dividend declared (in dollars per share)								$ 3.00		$ 1.50		$ 2.50
Dividend paid (in dollars per share)							$ 3.00		$ 1.50		$ 2.50
RLI Corp. Long-Term Incentive Plan (LTIP) and Omnibus Stock Plan
Stock options and stock plans
Award vesting period				5 years
Omnibus Stock Plan
Stock options and stock plans
Shares authorized for grant															3,000,000
Stock options granted to date (in shares)				2,458,059
RLI Corp. Long-Term Incentive Plan (LTIP)
Stock options and stock plans
Shares authorized for grant				4,000,000
Stock options granted to date (in shares)				2,824,500
Age and period of service of the participant to be eligible for retirement				75 years
Weighted Number of Options Outstanding
Options granted (in shares)				512,000
Outside Directors' Stock Option Plan (the director's plan)
Aggregate Intrinsic Value
Stock-based compensation expenses (in dollars)													100,000	100,000
Weighted average grant date assumptions and weighted average fair value
Restricted shares issued per recipient (in dollars)													$ 10,000	$ 10,000
Restricted shares issued													2,097	2,320
Restriction period													1 year