SEGMENT INFORMATION (Segments) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net premiums earned									$ 930,890	$ 828,330	$ 754,846
Investment income, net of investment expenses									100,781	104,609	112,799
Net realized investment gains									2,846	7,270	8,695
Other income (loss)									401	1,685	702
Total revenues	$ 275,956	$ 264,560	$ 255,918	$ 238,484	$ 250,452	$ 235,865	$ 232,673	$ 222,904	1,034,918	941,894	877,042
Benefit, losses and expenses									913,467	865,431	775,140
Income before income taxes	43,263	26,824	19,533	31,831	50,355	(2,845)	13,056	15,897	121,451	76,463	101,902
Income tax expense									32,325	17,326	25,762
Net income	30,895	$ 19,534	$ 15,018	$ 23,679	34,796	$ 325	$ 10,685	$ 13,331	89,126	59,137	76,140
Total assets	3,890,376				3,856,689				3,890,376	3,856,689	3,720,672
Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned									851,695	766,939	694,192
Total revenues									899,271	816,263	746,872
Income before income taxes									115,370	66,025	88,719
Income tax expense									30,050	13,649	21,263
Net income									85,320	52,376	67,456
Total assets	2,280,674				2,127,623				2,280,674	2,127,623	1,995,069
Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned									79,984	61,921	61,146
Total revenues									135,647	125,631	130,170
Income before income taxes									6,081	10,438	13,183
Income tax expense									2,275	3,677	4,499
Net income									3,806	6,761	8,684
Total assets	1,609,702				1,729,066				1,609,702	1,729,066	1,725,603
Operating Segments [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned									851,695	766,939	694,192
Investment income, net of investment expenses									46,606	44,219	46,279
Net realized investment gains									1,124	4,177	6,260
Other income (loss)									(107)	910	88
Total revenues									899,318	816,245	746,819
Benefit, losses and expenses									784,691	750,768	658,645
Total net income before eliminations									114,627	65,477	88,174
Total assets	2,490,138				2,360,764				2,490,138	2,360,764	2,218,464
Operating Segments [Member] | Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned									79,984	61,921	61,146
Investment income, net of investment expenses									54,222	60,373	66,467
Net realized investment gains									1,722	3,093	2,434
Other income (loss)									508	774	614
Total revenues									136,436	126,161	130,661
Benefit, losses and expenses									129,771	115,361	117,159
Total net income before eliminations									6,665	10,800	13,502
Intersegment Elimination [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues									(47)	18	53
Intersegment eliminations									743	548	545
Total assets	$ (209,464)				$ (233,141)				(209,464)	(233,141)	(223,395)
Intersegment Elimination [Member] | Life Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues									(789)	(530)	(491)
Intersegment eliminations									$ (584)	$ (362)	$ (319)