Investments - Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investments [Abstract]
Due in one year or less, Amortized Cost	$ 33,684	$ 44,341
Due in one year or less, Fair Value	33,718	44,503
Due after one year through five years, Amortized Cost	0	0
Due after one year through five years, Fair Value	0	0
Amortized Costs	33,684	44,341
Fair Value	$ 33,718	$ 44,503