Investments - Contractual Maturities of Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Amortized Cost
Due in one year or less	$ 184,930
Due after one year through five years	9,448
Due after ten years through fifteen years	98
Amortized Cost	194,476
Preferred stock	265
Restricted investments	5,651
Amortized Cost	200,392	$ 199,429
Fair Value
Due in one year or less	184,949
Due after one year through five years	8,359
Due after ten years through fifteen years	81
Fair Value	193,389
Preferred stock	148
Restricted investments	5,651
Fair Value	$ 199,188	$ 198,312