Fair Value Measurements - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Marketable Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Mature in one year or less, Amortized cost	$ 272,619
Mature after one year through two years, Amortized cost	14,496
Marketable securities, Amortized cost	287,115	$ 280,770
Mature in one year or less, Estimated Fair Value	272,500
Mature after one year through two years, Estimated Fair Value	14,474
Marketable securities, Estimated Fair Value	$ 286,974	$ 280,589