SCHEDULE III-SUPPLEMENTARY INSURANCE INFORMATION (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplementary insurance information
Deferred policy acquisition costs	$ 69,829	$ 65,123	$ 61,508
Unpaid losses and settlement expenses, gross	1,103,785	1,121,040	1,129,433
Unearned premiums, gross	422,094	401,412	392,081
Net premiums earned	700,161	687,375	630,802
Incurred losses and settlement expenses
Current accident year	364,472	361,451	332,282
Prior accident years	(65,427)	(64,842)	(72,481)
Policy acquisition costs	241,078	229,283	210,651
Other operating expenses	51,480	54,464	53,557
Net premiums written	721,971	703,152	666,322
Casualty segment
Supplementary insurance information
Deferred policy acquisition costs	35,464	31,334	28,553
Unpaid losses and settlement expenses, gross	993,717	964,699	947,677
Unearned premiums, gross	260,227	237,117	228,907
Net premiums earned	412,248	382,105	324,022
Incurred losses and settlement expenses
Current accident year	264,068	251,958	210,665
Prior accident years	(45,654)	(52,825)	(61,805)
Policy acquisition costs	119,529	108,747	93,463
Other operating expenses	28,042	28,284	26,107
Net premiums written	435,409	395,853	362,459
Property segment
Supplementary insurance information
Deferred policy acquisition costs	13,332	13,827	14,275
Unpaid losses and settlement expenses, gross	77,584	120,858	146,122
Unearned premiums, gross	88,808	94,092	97,116
Net premiums earned	170,924	197,776	200,141
Incurred losses and settlement expenses
Current accident year	81,699	90,712	103,544
Prior accident years	(11,848)	(1,123)	(7,273)
Policy acquisition costs	57,214	58,646	58,650
Other operating expenses	14,834	16,623	17,616
Net premiums written	166,659	195,580	196,467
Surety segment
Supplementary insurance information
Deferred policy acquisition costs	21,033	19,962	18,680
Unpaid losses and settlement expenses, gross	32,484	35,483	35,634
Unearned premiums, gross	73,059	70,203	66,058
Net premiums earned	116,989	107,494	106,639
Incurred losses and settlement expenses
Current accident year	18,705	18,781	18,073
Prior accident years	(7,925)	(10,894)	(3,403)
Policy acquisition costs	64,335	61,890	58,538
Other operating expenses	8,604	9,557	9,834
Net premiums written	$ 119,903	$ 111,719	$ 107,396