Investments - Contractual Maturities of Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Amortized Cost
Due in one year or less	$ 174,367
Due after one year through five years	19,987
Due after ten years through fifteen years	99
Amortized Cost	194,453
Preferred stock	22,930
Restricted investments	5,653
Amortized Cost	223,036	$ 199,429
Fair Value
Due in one year or less	174,564
Due after one year through five years	18,929
Due after ten years through fifteen years	83
Fair Value	193,576
Preferred stock	22,694
Restricted investments	5,653
Fair Value	$ 221,923	$ 198,312