Fair Value Measurements - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Marketable Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Mature in one year or less, Amortized cost	$ 281,796
Mature after one year through two years, Amortized cost	6,478
Marketable securities, Amortized cost	288,274	$ 280,770
Mature in one year or less, Estimated Fair Value	281,848
Mature after one year through two years, Estimated Fair Value	6,479
Marketable securities, Estimated Fair Value	$ 288,327	$ 280,589