Fair Value (Details 3) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair value by pricing source
Available-for-sale securities	$ 758,713	$ 713,291
Fair value measurements on a recurring basis
Fair value by pricing source
Available-for-sale securities	758,713	713,291
Total	763,529	717,703
Fair value measurements on a recurring basis | Fixed maturities
Fair value by pricing source
Available-for-sale securities	745,961	707,341
Fair value measurements on a recurring basis | Fixed maturities | Priced via market comparables/broker quotes
Fair value by pricing source
Available-for-sale securities	2,200
Fair value measurements on a recurring basis | Fixed maturities | Priced via pricing services
Fair value by pricing source
Available-for-sale securities	743,761
Fair value measurements on a recurring basis | Nonredeemable preferred stock
Fair value by pricing source
Available-for-sale securities	12,752
Fair value measurements on a recurring basis | Nonredeemable preferred stock | Priced via pricing services
Fair value by pricing source
Available-for-sale securities	12,752
Fair value measurements on a recurring basis | Real estate
Fair value by pricing source
Other investments	4,816	4,412
Fair value measurements on a recurring basis | Real estate | Priced via unobservable inputs
Fair value by pricing source
Other investments	4,816
Fair value measurements on a recurring basis | Level 1
Fair value by pricing source
Available-for-sale securities	2,015	5,950
Total	2,015	5,950
Fair value measurements on a recurring basis | Level 1 | Fixed maturities
Fair value by pricing source
Available-for-sale securities	0	0
Fair value measurements on a recurring basis | Level 1 | Fixed maturities | Priced via market comparables/broker quotes
Fair value by pricing source
Available-for-sale securities	0
Fair value measurements on a recurring basis | Level 1 | Fixed maturities | Priced via pricing services
Fair value by pricing source
Available-for-sale securities	0
Fair value measurements on a recurring basis | Level 1 | Nonredeemable preferred stock
Fair value by pricing source
Available-for-sale securities	2,015
Fair value measurements on a recurring basis | Level 1 | Nonredeemable preferred stock | Priced via pricing services
Fair value by pricing source
Available-for-sale securities	2,015
Fair value measurements on a recurring basis | Level 2
Fair value by pricing source
Available-for-sale securities	746,619	697,989
Total	746,619	697,989
Fair value measurements on a recurring basis | Level 2 | Fixed maturities
Fair value by pricing source
Available-for-sale securities	735,882	697,989
Fair value measurements on a recurring basis | Level 2 | Fixed maturities | Priced via market comparables/broker quotes
Fair value by pricing source
Available-for-sale securities	0
Fair value measurements on a recurring basis | Level 2 | Fixed maturities | Priced via pricing services
Fair value by pricing source
Available-for-sale securities	735,882
Fair value measurements on a recurring basis | Level 2 | Nonredeemable preferred stock
Fair value by pricing source
Available-for-sale securities	10,737
Fair value measurements on a recurring basis | Level 2 | Nonredeemable preferred stock | Priced via pricing services
Fair value by pricing source
Available-for-sale securities	10,737
Fair value measurements on a recurring basis | Level 3
Fair value by pricing source
Available-for-sale securities	10,079	9,352
Total	10,079	9,352
Fair value measurements on a recurring basis | Level 3 | Priced via market comparables/broker quotes
Fair value by pricing source
Available-for-sale securities	10,100
Fair value measurements on a recurring basis | Level 3 | Fixed maturities
Fair value by pricing source
Available-for-sale securities	10,079	$ 9,352
Fair value measurements on a recurring basis | Level 3 | Fixed maturities | Priced via market comparables/broker quotes
Fair value by pricing source
Available-for-sale securities	2,200
Fair value measurements on a recurring basis | Level 3 | Fixed maturities | Priced via pricing services
Fair value by pricing source
Available-for-sale securities	7,879
Fair value measurements on a recurring basis | Level 3 | Nonredeemable preferred stock
Fair value by pricing source
Available-for-sale securities	0
Fair value measurements on a recurring basis | Level 3 | Nonredeemable preferred stock | Priced via pricing services
Fair value by pricing source
Available-for-sale securities	0
Fair value measurements on a nonrecurring basis
Fair value by pricing source
Total	$ 0