INCOME TAXES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Tax discounting of claim reserves	$ 17,866	$ 19,609
Unearned premium offset	25,848	24,322
Deferred compensation	6,231	6,143
Stock option expense	4,482	5,046
Other	657	453
Deferred tax assets before allowance	55,084	55,573
Total deferred tax assets	55,084	55,573
Deferred tax liabilities:
Net unrealized appreciation of securities	67,740	92,562
Deferred policy acquisition costs	24,440	22,793
Book/tax depreciation	4,613	3,610
Intangible assets from CBIC acquisition	3,392	3,594
Undistributed earnings of unconsolidated investees	17,888	14,728
Other	1,004	571
Total deferred tax liabilities	119,077	137,858
Net deferred tax liability	$ (63,993)	$ (82,285)
U.S. federal tax rate (as a percent)	35.00%	35.00%	35.00%
Reconciliation of income tax expense reported to amount computed by applying the U.S. federal tax rate
Provision for income taxes at the statutory rate of 35%	$ 68,839	$ 66,320	$ 61,483
Increase (reduction) in taxes resulting from:
Dividends received deduction	(2,278)	(2,390)	(2,490)
ESOP dividends paid deduction	(3,377)	(4,473)	(2,532)
Tax-exempt interest income	(4,214)	(4,118)	(3,758)
Unconsolidated investee dividends		(1,848)	(3,696)
Other items, net	168	551	404
Total tax expense	$ 59,138	$ 54,042	$ 49,411
Effective tax rates (as a percent)	30.10%	28.50%	28.10%
Effective rate reduction due to dividends paid to ESOP (as a percent)	1.70%	2.40%	1.40%
Capital gains rate (as a percent)	35.00%
Dividend received		$ 6,600	$ 13,200
Lower tax rate (as a percent)		7.00%	7.00%
Effective rate reduction due to dividend received (as a percent)		1.00%	2.10%
Expected effective tax rate when deferred items reverse in future years (as a percent)	35.00%
Federal and state income taxes paid	$ 44,200	$ 48,500	$ 36,800