Investments - Contractual Maturities of Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized Cost
Due in one year or less	$ 3,932
Due after one year through five years	124,177
Due after ten years through fifteen years	91
Amortized Cost	128,200
Amortized Cost	174,831	$ 177,280
Fair Value
Due in one year or less	3,470
Due after one year through five years	129,266
Due after ten years through fifteen years	49
Fair Value	132,785
Fair Value	180,071	181,361
Preferred stock
Amortized Cost
Securities without maturity date, amortized cost	40,525
Amortized Cost	40,525	36,048
Fair Value
Securities without maturity date, fair value	41,066
Fair Value	41,066	36,593
Common Stock
Amortized Cost
Securities without maturity date, amortized cost	1,662
Amortized Cost	1,662
Fair Value
Securities without maturity date, fair value	1,772
Fair Value	1,772
Restricted investments
Amortized Cost
Securities without maturity date, amortized cost	4,444
Amortized Cost	4,444	5,642
Fair Value
Securities without maturity date, fair value	4,448
Fair Value	$ 4,448	$ 5,636