Investments - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Amortized Cost
Mature in one year or less	$ 182,069	$ 186,311
Mature after one year through three years	112,281	106,377
Mature in more than three years	7,908	8,139
Total	302,258	300,827
Estimated Fair Value
Mature in one year or less	182,035	186,118
Mature after one year through three years	112,340	106,086
Mature in more than three years	7,867	8,061
Total	$ 302,242	$ 300,265