Reinsurance (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Premiums Written [Abstract]
Direct									$ 284,200	$ 274,101	$ 249,699
Ceded on direct									(105,292)	(84,130)	(75,907)
Net direct									178,908	189,971	173,792
Assumed									57,086	60,425	46,103
Ceded on assumed									(2,316)	(1,913)	(1,250)
Net assumed									54,770	58,512	44,853
Net									233,678	248,483	218,645
Premium Earned [Abstract]
Direct									287,982	270,002	245,912
Ceded on direct									(101,396)	(83,580)	(71,869)
Net direct									186,586	186,422	174,043
Assumed									53,191	60,061	41,945
Ceded on assumed									(2,316)	(1,913)	(1,250)
Net assumed									50,875	58,148	40,695
Net	61,402	54,853	59,655	61,551	64,196	60,429	62,344	57,601	237,461	244,570	214,738
Net losses and loss expenses incurred reduced by ceded reinsurance recoveries									90,899	56,600	15,318
Net losses and loss expense incurred from reinsurance assumed from non-affiliates									16,486	88,934	38,318
Retrocessional recoveries									20,000
Components of reinsurance recoverable [Abstract]
Case unpaid losses, net of valuation allowance	105,940				72,914				105,940	72,914
Incurred but not reported unpaid losses and loss expenses	59,421				56,262				59,421	56,262
Paid losses and loss expenses	2,506				3,043				2,506	3,043
Unearned premiums	7,324				6,185				7,324	6,185
Reinsurance recoverable	$ 175,191				$ 138,404				$ 175,191	$ 138,404