OPERATING SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
REVENUES
Net premiums earned	$ 183,595	$ 179,448	$ 540,739	$ 520,790
Net investment income	13,504	13,964	39,922	40,890
Net realized gains	9,252	7,534	23,362	25,622
Consolidated revenue	206,351	200,946	604,023	587,302
NET EARNINGS (LOSSES)
Net underwriting income	10,604	33,593	57,924	86,067
Net investment income	13,504	13,964	39,922	40,890
Net realized gains	9,252	7,534	23,362	25,622
General corporate expense and interest on debt	(4,099)	(3,815)	(12,955)	(12,520)
Equity in earnings of unconsolidated investees	1,881	661	10,823	11,041
Earnings before income taxes	31,142	51,937	119,076	151,100
Income tax expense	8,879	16,029	36,343	47,409
Net earnings	22,263	35,908	82,733	103,691
Casualty segment
REVENUES
Net premiums earned	115,619	105,160	336,572	305,842
NET EARNINGS (LOSSES)
Net underwriting income	259	13,651	20,490	38,124
Property segment
REVENUES
Net premiums earned	37,532	44,685	114,011	128,084
NET EARNINGS (LOSSES)
Net underwriting income	468	9,216	13,911	22,220
Surety segment
REVENUES
Net premiums earned	30,444	29,603	90,156	86,864
NET EARNINGS (LOSSES)
Net underwriting income	$ 9,877	$ 10,726	$ 23,523	$ 25,723