SCHEDULE III-SUPPLEMENTARY INSURANCE INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Supplementary insurance information
Deferred policy acquisition costs	$ 61,508	$ 52,344	$ 52,105
Unpaid losses and settlement expenses, gross	1,129,433	1,158,483	1,150,714
Unearned premiums, gross	392,081	369,346	341,267
Net premiums earned	630,802	576,571	538,452
Incurred losses and settlement expenses
Current accident year	332,282	336,228	310,145
Prior accident years	(72,481)	(64,583)	(110,061)
Policy acquisition costs	210,651	196,362	183,868
Other operating expenses	53,557	44,971	44,312
Net premiums written	666,322	593,086	549,638
Casualty segment
Supplementary insurance information
Deferred policy acquisition costs	28,553	19,673	18,507
Unpaid losses and settlement expenses, gross	947,677	955,730	973,077
Unearned premiums, gross	228,907	199,672	171,768
Net premiums earned	324,022	267,697	236,198
Incurred losses and settlement expenses
Current accident year	210,665	184,555	168,983
Prior accident years	(61,805)	(40,449)	(83,892)
Policy acquisition costs	93,463	76,765	67,495
Other operating expenses	26,107	21,387	22,215
Net premiums written	362,459	284,058	238,611
Property segment
Supplementary insurance information
Deferred policy acquisition costs	14,275	14,523	14,474
Unpaid losses and settlement expenses, gross	146,122	169,250	133,861
Unearned premiums, gross	97,116	103,854	103,346
Net premiums earned	200,141	202,402	203,660
Incurred losses and settlement expenses
Current accident year	103,544	132,507	120,422
Prior accident years	(7,273)	(16,800)	(18,453)
Policy acquisition costs	58,650	60,070	57,878
Other operating expenses	17,616	14,933	13,481
Net premiums written	196,467	202,971	210,904
Surety segment
Supplementary insurance information
Deferred policy acquisition costs	18,680	18,148	19,124
Unpaid losses and settlement expenses, gross	35,634	33,503	43,776
Unearned premiums, gross	66,058	65,820	66,153
Net premiums earned	106,639	106,472	98,594
Incurred losses and settlement expenses
Current accident year	18,073	19,166	20,740
Prior accident years	(3,403)	(7,334)	(7,716)
Policy acquisition costs	58,538	59,527	58,495
Other operating expenses	9,834	8,651	8,616
Net premiums written	$ 107,396	$ 106,057	$ 100,123