Fair Value Measurements - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Marketable Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Mature in one year or less, Amortized cost	$ 271,960
Mature after one year through two years, Amortized cost	17,180
Marketable securities, Amortized cost	289,140	$ 280,770
Mature in one year or less, Estimated Fair Value	271,985
Mature after one year through two years, Estimated Fair Value	17,179
Marketable securities, Estimated Fair Value	$ 289,164	$ 280,589