Cash, Cash Equivalents, and Short-Term Investments - Summary of Cost and Estimated Fair Value of Short-Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Short Term Investments [Abstract]
Amortized Cost of short-term investments, Due within one year	$ 83,416
Amortized Cost of short-term investments, Due within two years	65,781
Short-term investments, Amortized Cost	149,197	$ 96,853
Estimated fair value of short-term investments, Due within one year	83,357
Estimated fair value of short-term investments, Due within two years	65,657
Short-term investments, Estimated Fair Value	$ 149,014	$ 96,555	[1]

[1] The Condensed Consolidated Balance Sheet as of December 31, 2015 has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements.