Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Premiums Written [Abstract]
Direct									$ 395,625	$ 366,668	$ 343,200
Ceded on direct									(131,166)	(128,338)	(118,942)
Net direct									264,459	238,330	224,258
Assumed									7,379	16,885	39,188
Ceded on assumed									(86)	(562)	(1,275)
Net assumed									7,293	16,323	37,913
Net									271,752	254,653	262,171
Premium Earned [Abstract]
Direct									394,679	370,499	342,656
Ceded on direct									(129,926)	(128,135)	(117,973)
Net direct									264,753	242,364	224,683
Assumed									11,344	21,533	38,219
Ceded on assumed									(86)	(562)	(1,275)
Net assumed									11,258	20,971	36,944
Net	$ 69,141	$ 71,235	$ 68,726	$ 66,909	$ 65,995	$ 65,445	$ 65,449	$ 66,446	276,011	263,335	261,627
Net losses and loss expenses incurred reduced by ceded reinsurance recoveries									108,656	75,581	105,891
Net losses and loss expense incurred from reinsurance assumed from non-affiliates									14,746	13,492	$ 20,288
Components of reinsurance recoverable [Abstract]
Case unpaid losses, net of valuation allowance	126,244				120,320				126,244	120,320
Incurred but not reported unpaid losses and loss expenses	123,819				90,578				123,819	90,578
Paid losses and loss expenses	1,760				2,452				1,760	2,452
Unearned premiums	3,201				2,538				3,201	2,538
Reinsurance recoverable	$ 255,024				$ 215,888				$ 255,024	$ 215,888