Reinsurance (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Premiums Written [Abstract]
Direct									$ 343,200	$ 314,784	$ 284,200
Ceded on direct									(118,942)	(112,967)	(105,292)
Net direct									224,258	201,817	178,908
Assumed									39,188	54,692	57,086
Ceded on assumed									(1,275)	(2,825)	(2,316)
Net assumed									37,913	51,867	54,770
Net									262,171	253,684	233,678
Premium Earned [Abstract]
Direct									342,656	313,842	287,982
Ceded on direct									(117,973)	(111,057)	(101,396)
Net direct									224,683	202,785	186,586
Assumed									38,219	52,783	53,191
Ceded on assumed									(1,275)	(2,825)	(2,316)
Net assumed									36,944	49,958	50,875
Net	68,933	65,947	62,905	63,842	65,422	64,448	61,775	61,098	261,627	252,743	237,461
Net losses and loss expenses incurred reduced by ceded reinsurance recoveries									105,891	107,321	90,899
Net losses and loss expense incurred from reinsurance assumed from non-affiliates									23,163	20,014	16,486
Retrocessional recoveries											20,000
Components of reinsurance recoverable [Abstract]
Case unpaid losses, net of valuation allowance	143,403				133,484				143,403	133,484
Incurred but not reported unpaid losses and loss expenses	66,325				52,157				66,325	52,157
Paid losses and loss expenses	6,910				4,126				6,910	4,126
Unearned premiums	3,583				5,801				3,583	5,801
Reinsurance recoverable	$ 220,221				$ 195,568				$ 220,221	$ 195,568