Cash, Cash Equivalents, and Short-Term Investments - Summary of Cash, Cash Equivalents and Short-Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	$ 110,019	$ 168,255
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	2	3
Cash and cash equivalents, Fair Value	110,017	168,252
Short-term investments, Amortized Cost	149,197	96,853
Short-term investments, Gross Unrealized Gains	16	2
Short-term investments, Gross Unrealized Losses	199	300
Short-term investments, Estimated Fair Value	149,014	96,555	[1]
Cash [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	61,609	57,906
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	61,609	57,906
Bank Deposits [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost		10,253
Cash and cash equivalents, Gross Unrealized Gains		0
Cash and cash equivalents, Gross Unrealized Losses		0
Cash and cash equivalents, Fair Value		10,253
Short-term investments, Amortized Cost	10,367	10,263
Short-term investments, Gross Unrealized Gains	0	0
Short-term investments, Gross Unrealized Losses	0	0
Short-term investments, Estimated Fair Value	10,367	10,263
Commercial Paper [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	10,246	13,896
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	2	3
Cash and cash equivalents, Fair Value	10,244	13,893
Short-term investments, Amortized Cost	19,200
Short-term investments, Gross Unrealized Gains	0
Short-term investments, Gross Unrealized Losses	16
Short-term investments, Estimated Fair Value	19,184
Money Market Funds [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	38,164	86,200
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	38,164	86,200
Corporate Debt Obligations [Member]
Schedule of Investments [Line Items]
Short-term investments, Amortized Cost	100,628	86,590
Short-term investments, Gross Unrealized Gains	8	2
Short-term investments, Gross Unrealized Losses	176	300
Short-term investments, Estimated Fair Value	100,460	$ 86,292
US Government Agencies [Member]
Schedule of Investments [Line Items]
Short-term investments, Amortized Cost	19,002
Short-term investments, Gross Unrealized Gains	8
Short-term investments, Gross Unrealized Losses	7
Short-term investments, Estimated Fair Value	$ 19,003

[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.