Marketable Securities - Summary of Amortized Cost and Estimated Fair Value of Marketable Securities by Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 156,951	$ 196,817
Gross Unrealized Gains	26	4
Gross Unrealized Losses	(99)	(347)
Estimated Fair Value	156,878	196,474
Due in one year or less
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	145,592	164,147
Gross Unrealized Gains	18	2
Gross Unrealized Losses	(89)	(221)
Estimated Fair Value	145,521	163,928
Due after one year
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,359	32,670
Gross Unrealized Gains	8	2
Gross Unrealized Losses	(10)	(126)
Estimated Fair Value	$ 11,357	$ 32,546