STATUTORY INFORMATION AND DIVIDEND RESTRICTIONS (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) company	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Statutory information and dividend restrictions
Number of insurance companies | company	3
Equity	$ 823,572	$ 823,469	$ 845,062	$ 828,966
Remaining unrestricted equity, liquid assets	45,900
Fair Value of Investment in Affiliate Included in Statutory Surplus	104,400	117,500	86,100
Cost Basis of Investment in Affiliate Included in Statutory Surplus	64,600
RLI Ins.
Statutory information and dividend restrictions
Authorized control level RBC	127,000	123,600	118,400
Selected information for insurance subsidiaries
Consolidated surplus, statutory basis	$ 860,000	865,300	849,300
Dividend restriction as percentage of policyholder surplus	10.00%
Payments of Ordinary Dividends	$ 123,600	125,000	185,000
Extraordinary dividend paid after seeking and receiving approval from the Illinois regulatory authorities	0	0	0
Insurance subsidiaries
Selected information for insurance subsidiaries
Consolidated net income, statutory basis	128,165	178,502	176,664
Consolidated surplus, statutory basis	$ 859,976	$ 865,268	$ 849,297