Investments Net Investment Income by Major Category (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Investment Income [Line Items]
Net investment income	$ 10,679	$ 9,212	$ 6,795
Investment expenses	(587)	(267)	(312)
Investment Income, Net	10,092	8,945	6,483
Debt Securities [Member]
Net Investment Income [Line Items]
Net investment income	9,170	8,092	5,866
Equity Securities
Net Investment Income [Line Items]
Net investment income	996	859	734
Cash, Cash Equivalents And Short-Term Investments [Member]
Net Investment Income [Line Items]
Net investment income	141	25	9
Partnership Interest [Member]
Net Investment Income [Line Items]
Net investment income	352	222	166
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Net Investment Income [Line Items]
Net investment income	$ 20	$ 14	$ 20