Investments (Details) $ in Thousands	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($) item
Securities available-for-sale
Fixed maturity securities, Cost or Amortized Cost	$ 1,142,663	$ 1,063,971
Fixed maturity securities, Gross Unrealized Gains	22,140	30,608
Fixed maturity securities, Non-OTTI Gross Unrealized Losses	(10,534)	(12,942)
Fixed maturity securities, Estimated Fair Value	1,154,269	1,081,637
Equity securities, Cost or Amortized Cost	92,326	102,541
Equity securities, Gross Unrealized Gains	15,504	13,498
Equity securities, Non-OTTI Gross Unrealized Losses	(2,735)	(5,835)
Equity securities, Estimated Fair Value	105,095	110,204
Other invested assets, Cost or Amortized Cost	21,142	17,602
Other invested assets, Estimated Fair Value	21,142	17,602
Cost or Amortized Cost	1,256,131	1,184,114
Gross Unrealized Gains	37,644	44,106
Gross Non-OTTI Unrealized Losses	(13,269)	(18,777)
Estimated Fair Value	$ 1,280,506	$ 1,209,443
Number of securities in an unrealized loss position | item	343	514
U.S. Treasury securities
Securities available-for-sale
Fixed maturity securities, Cost or Amortized Cost	$ 302	$ 1,805
Fixed maturity securities, Non-OTTI Gross Unrealized Losses		(4)
Fixed maturity securities, Estimated Fair Value	302	1,801
Obligations of states and political subdivisions
Securities available-for-sale
Fixed maturity securities, Cost or Amortized Cost	382,811	377,188
Fixed maturity securities, Gross Unrealized Gains	11,534	21,160
Fixed maturity securities, Non-OTTI Gross Unrealized Losses	(3,912)	(426)
Fixed maturity securities, Estimated Fair Value	390,433	397,922
Residential mortgage-backed securities
Securities available-for-sale
Fixed maturity securities, Cost or Amortized Cost	252,031	237,896
Fixed maturity securities, Gross Unrealized Gains	3,256	5,188
Fixed maturity securities, Non-OTTI Gross Unrealized Losses	(2,656)	(1,628)
Fixed maturity securities, Estimated Fair Value	252,631	241,456
Commercial mortgage-backed securities
Securities available-for-sale
Fixed maturity securities, Cost or Amortized Cost	35,695	28,851
Fixed maturity securities, Gross Unrealized Gains	191	30
Fixed maturity securities, Non-OTTI Gross Unrealized Losses	(432)	(218)
Fixed maturity securities, Estimated Fair Value	35,454	28,663
Other asset-backed securities
Securities available-for-sale
Fixed maturity securities, Cost or Amortized Cost	70,411	24,037
Fixed maturity securities, Gross Unrealized Gains	89	39
Fixed maturity securities, Non-OTTI Gross Unrealized Losses	(90)	(145)
Fixed maturity securities, Estimated Fair Value	70,410	23,931
Corporate and other securities
Securities available-for-sale
Fixed maturity securities, Cost or Amortized Cost	401,413	394,194
Fixed maturity securities, Gross Unrealized Gains	7,070	4,191
Fixed maturity securities, Non-OTTI Gross Unrealized Losses	(3,444)	(10,521)
Fixed maturity securities, Estimated Fair Value	$ 405,039	$ 387,864