Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	$ 713,291	$ 599,941
Other investments:
Contributions made to the funds	578	928	$ 1,123
Distributions received from the funds	16,113	26,735	$ 28,613
Fair value measurements on a recurring basis
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	713,291	599,941
Total	717,703	604,467
Fair value measurements on a recurring basis | Fixed maturities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	707,341	587,209
Fair value measurements on a recurring basis | U.S. treasury
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	5,031
Fair value measurements on a recurring basis | Government sponsored entities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	2,026
Fair value measurements on a recurring basis | States & political subdivisions
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	253,132	231,847
Fair value measurements on a recurring basis | Corporate debt securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	322,948	250,333
Fair value measurements on a recurring basis | Residential mortgage-backed securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	16,102	13,513
Fair value measurements on a recurring basis | Commercial mortgage-backed securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	36,849	37,571
Fair value measurements on a recurring basis | Collateralized debt obligations
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	69,253	51,745
Fair value measurements on a recurring basis | Other debt securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	2,000	2,200
Fair value measurements on a recurring basis | Common stock
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	5,950	12,732
Fair value measurements on a recurring basis | Real estate
Consolidated fair value measurements on a recurring basis by asset class and level of input
Other investments	4,412	4,526
Fair value measurements on a recurring basis | Level 1
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	5,950	12,732
Total	5,950	12,732
Fair value measurements on a recurring basis | Level 1 | Fixed maturities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 1 | U.S. treasury
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0
Fair value measurements on a recurring basis | Level 1 | Government sponsored entities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0
Fair value measurements on a recurring basis | Level 1 | States & political subdivisions
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 1 | Corporate debt securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 1 | Residential mortgage-backed securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 1 | Commercial mortgage-backed securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 1 | Collateralized debt obligations
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 1 | Other debt securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 1 | Common stock
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	5,950	12,732
Fair value measurements on a recurring basis | Level 2
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	697,989	578,563
Total	697,989	578,563
Fair value measurements on a recurring basis | Level 2 | Fixed maturities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	697,989	578,563
Fair value measurements on a recurring basis | Level 2 | U.S. treasury
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	5,031
Fair value measurements on a recurring basis | Level 2 | Government sponsored entities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	2,026
Fair value measurements on a recurring basis | Level 2 | States & political subdivisions
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	253,132	231,847
Fair value measurements on a recurring basis | Level 2 | Corporate debt securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	313,596	250,264
Fair value measurements on a recurring basis | Level 2 | Residential mortgage-backed securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	16,102	13,513
Fair value measurements on a recurring basis | Level 2 | Commercial mortgage-backed securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	36,849	37,571
Fair value measurements on a recurring basis | Level 2 | Collateralized debt obligations
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	69,253	43,168
Fair value measurements on a recurring basis | Level 2 | Other debt securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	2,000	2,200
Fair value measurements on a recurring basis | Level 2 | Common stock
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 3
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	9,352	8,646
Total	9,352	8,646
Fair value measurements on a recurring basis | Level 3 | Fixed maturities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	9,352	8,646
Fair value measurements on a recurring basis | Level 3 | U.S. treasury
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0
Fair value measurements on a recurring basis | Level 3 | Government sponsored entities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0
Fair value measurements on a recurring basis | Level 3 | States & political subdivisions
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 3 | Corporate debt securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	9,352	69
Fair value measurements on a recurring basis | Level 3 | Residential mortgage-backed securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 3 | Commercial mortgage-backed securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 3 | Collateralized debt obligations
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	8,577
Fair value measurements on a recurring basis | Level 3 | Other debt securities
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 3 | Common stock
Consolidated fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 3 | Real estate
Other investments:
Contributions made to the funds	0	0
Distributions received from the funds	900	3,500
Unfunded commitments	$ 300	$ 600
Fair value measurements on a recurring basis | Level 3 | Real estate | Minimum
Other investments:
Underlying assets, liquidation period from inception of fund (in years)	5 years	5 years
Fair value measurements on a recurring basis | Level 3 | Real estate | Maximum
Other investments:
Underlying assets, liquidation period from inception of fund (in years)	10 years	10 years