Reinsurance - Effects of Reinsurance and Assumption Transactions (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Written premiums:
Direct									$ 86,251	$ 89,915	$ 90,503
Assumed									28,033	25,008	3,247
Ceded									(23,044)	(14,994)	(14,076)
Net written premiums	$ 27,439	$ 18,395	$ 23,082	$ 22,324	$ 27,069	$ 24,634	$ 26,176	$ 22,050	91,240	99,929	79,674
Earned premiums:
Direct									87,656	90,660	82,614
Assumed									27,081	14,053	6,602
Ceded									(23,008)	(15,086)	(22,451)
Net earned premiums	25,433	17,659	24,497	24,140	24,463	23,380	21,675	20,109	91,729	89,627	66,765
Loss and loss adjustment expenses:
Direct									79,035	59,940	43,989
Assumed									19,524	11,955	2,756
Ceded									(24,642)	(12,892)	(7,863)
Net Loss and loss adjustment expenses	15,042	$ 26,468	$ 16,674	$ 15,733	$ 18,181	$ 14,582	$ 13,541	$ 12,699	73,917	$ 59,003	$ 38,882
Reinsurance reinstatement cost	$ 806								$ 806