Summary of Significant Accounting Policies - Summary of Financial Assets Recognized at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 270,448	$ 30,000
Total	270,448	30,000
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	270,448	30,000
Total	$ 270,448	$ 30,000