OPERATING SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
REVENUES
Net premiums earned	$ 172,339	$ 168,604	$ 341,342	$ 329,736
Net investment income	13,431	13,982	26,926	27,564
Net realized gains	4,802	10,431	18,088	16,932
Consolidated revenue	190,572	193,017	386,356	374,232
NET EARNINGS (LOSSES)
Net underwriting income	34,836	26,569	52,474	49,101
Net investment income	13,431	13,982	26,926	27,564
Net realized gains	4,802	10,431	18,088	16,932
General corporate expense and interest on debt	(4,605)	(4,423)	(8,705)	(8,472)
Equity in earnings of unconsolidated investees	6,186	5,864	10,380	9,289
Earnings before income taxes	54,650	52,423	99,163	94,414
Income tax expense	17,465	16,698	31,380	29,720
Net earnings	37,185	35,725	67,783	64,694
Casualty segment
REVENUES
Net premiums earned	101,914	94,360	200,682	185,337
NET EARNINGS (LOSSES)
Net underwriting income	19,201	16,467	24,473	22,545
Property segment
REVENUES
Net premiums earned	41,281	48,791	83,399	92,109
NET EARNINGS (LOSSES)
Net underwriting income	4,828	2,293	13,004	11,971
Surety segment
REVENUES
Net premiums earned	29,144	25,453	57,261	52,290
NET EARNINGS (LOSSES)
Net underwriting income	$ 10,807	$ 7,809	$ 14,997	$ 14,585