STATUTORY INFORMATION AND DIVIDEND RESTRICTIONS (Details) - 10K (USD $)	12 Months Ended
	Dec. 31, 2014 company	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statutory information and dividend restrictions
Number of insurance companies	4
Equity	$ 845,062,000	$ 828,966,000	$ 796,363,000	$ 792,634,000
Remaining unrestricted equity, liquid assets	46,700,000
RLI Ins.
Statutory information and dividend restrictions
Authorized control level RBC	118,400,000	90,600,000	90,400,000
Selected information for insurance subsidiaries
Consolidated surplus, statutory basis	849,300,000	859,200,000	684,100,000
Dividend restriction as percentage of policyholder surplus	10.00%
Ordinary dividends paid	185,000,000	40,000,000	13,000,000
Extraordinary dividend paid after seeking and receiving approval from the Illinois regulatory authorities	0	0	125,000,000
Non restricted net assets	53,400,000
Mt. Hawley Insurance Company
Statutory information and dividend restrictions
Cost basis of RLI stock held by the subsidiary	64,600,000
Insurance subsidiaries
Selected information for insurance subsidiaries
Consolidated net income, statutory basis	176,664,000	122,550,000	125,672,000
Consolidated surplus, statutory basis	849,297,000	859,221,000	684,072,000
Common Stock | Mt. Hawley Insurance Company
Selected information for insurance subsidiaries
Consolidated surplus, statutory basis	$ 86,100,000	$ 64,000,000	$ 9,100,000