Investments - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Amortized Cost
Mature in one year or less	$ 179,418	$ 186,311
Mature after one year through three years	111,507	106,377
Mature in more than three years	11,860	8,139
Total	302,785	300,827
Estimated Fair Value
Mature in one year or less	179,473	186,118
Mature after one year through three years	111,730	106,086
Mature in more than three years	11,831	8,061
Total	$ 303,034	$ 300,265