Investments - Contractual Maturities of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Cost
Due in one year or less	$ 3,910
Due after one year through five years	131,581
Due after ten through fifteen years	99
Amortized Cost	135,590
Preferred stock	36,048
Restricted investments	5,642
Amortized Cost	177,280	$ 199,429
Fair Value
Due in one year or less	3,719
Due after one year through five years	135,344
Due after ten through fifteen years	69
Fair Value	139,132
Preferred stock	36,593
Restricted investments	5,636
Available-for-sale Securities	$ 181,361	$ 198,312