Fair Value (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	$ 653,635		$ 599,941
Other investments:
Contributions made to the funds	367	$ 597
Distributions received from the funds	11,246	$ 14,708
Fair value measurements on a recurring basis
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	653,635		599,941
Total	658,039		604,467
Fair value measurements on a recurring basis | Fixed maturities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	644,521		587,209
Fair value measurements on a recurring basis | States & political subdivisions
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	241,824		231,847
Fair value measurements on a recurring basis | Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	290,028		250,333
Fair value measurements on a recurring basis | Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	14,029		13,513
Fair value measurements on a recurring basis | Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	40,023		37,571
Fair value measurements on a recurring basis | Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	56,633		51,745
Fair value measurements on a recurring basis | Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	1,984		2,200
Fair value measurements on a recurring basis | Common stock
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	9,114		12,732
Trading securities	496
Fair value measurements on a recurring basis | Real estate
Fair value measurements on a recurring basis by asset class and level of input
Other investments	3,908		4,526
Fair value measurements on a recurring basis | Level 1
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	9,114		12,732
Total	9,610		12,732
Fair value measurements on a recurring basis | Level 1 | Fixed maturities
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 | States & political subdivisions
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
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
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
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
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
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
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	9,114		12,732
Trading securities	496
Fair value measurements on a recurring basis | Level 2
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	633,467		578,563
Total	633,467		578,563
Fair value measurements on a recurring basis | Level 2 | Fixed maturities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	633,467		578,563
Fair value measurements on a recurring basis | Level 2 | States & political subdivisions
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	241,824		231,847
Fair value measurements on a recurring basis | Level 2 | Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	281,177		250,264
Fair value measurements on a recurring basis | Level 2 | Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	14,029		13,513
Fair value measurements on a recurring basis | Level 2 | Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	39,020		37,571
Fair value measurements on a recurring basis | Level 2 | Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	55,433		43,168
Fair value measurements on a recurring basis | Level 2 | Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	1,984		2,200
Fair value measurements on a recurring basis | Level 2 | Common stock
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0		0
Trading securities	0
Fair value measurements on a recurring basis | Level 3
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	11,054		8,646
Total	11,054		8,646
Fair value measurements on a recurring basis | Level 3 | Fixed maturities
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	11,054		8,646
Fair value measurements on a recurring basis | Level 3 | States & political subdivisions
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
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	8,851		69
Fair value measurements on a recurring basis | Level 3 | Residential mortgage-backed securities
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
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	1,003		0
Fair value measurements on a recurring basis | Level 3 | Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	1,200		8,577
Fair value measurements on a recurring basis | Level 3 | Other debt securities
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
Fair value measurements on a recurring basis by asset class and level of input
Available-for-sale securities	0		0
Trading securities	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	700		3,500
Unfunded commitments	$ 300		$ 600
Minimum | Fair value measurements on a recurring basis | Level 3 | Real estate
Other investments:
Underlying assets, liquidation period from inception of fund (in years)	5 years		5 years
Maximum | Fair value measurements on a recurring basis | Level 3 | Real estate
Other investments:
Underlying assets, liquidation period from inception of fund (in years)	10 years		10 years