OPERATING SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
REVENUES
Net premiums earned	$ 179,448	$ 177,747	$ 520,790	$ 507,483
Net investment income	13,964	14,200	40,890	41,764
Net realized gains	7,534	5,708	25,622	22,640
Consolidated revenue	200,946	197,655	587,302	571,887
NET EARNINGS (LOSSES)
Net underwriting income	33,593	30,428	86,067	79,529
Net investment income	13,964	14,200	40,890	41,764
Net realized gains	7,534	5,708	25,622	22,640
General corporate expense and interest on debt	(3,815)	(4,657)	(12,520)	(13,129)
Equity in earnings of unconsolidated investees	661	2,915	11,041	12,204
Earnings before income taxes	51,937	48,594	151,100	143,008
Income tax expense	16,029	15,340	47,409	45,060
Net earnings	35,908	33,254	103,691	97,948
Casualty segment
REVENUES
Net premiums earned	105,160	96,181	305,842	281,518
NET EARNINGS (LOSSES)
Net underwriting income	13,651	13,786	38,124	36,331
Property segment
REVENUES
Net premiums earned	44,685	54,143	128,084	146,252
NET EARNINGS (LOSSES)
Net underwriting income	9,216	7,498	22,220	19,469
Surety segment
REVENUES
Net premiums earned	29,603	27,423	86,864	79,713
NET EARNINGS (LOSSES)
Net underwriting income	$ 10,726	$ 9,144	$ 25,723	$ 23,729