Cash, Cash Equivalents, and Short-Term Investments - Summary of Cash, Cash Equivalents and Short-Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	$ 163,935	$ 107,345
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	2
Cash and cash equivalents, Fair Value	163,935	107,343
Short-term investments, Amortized Cost	179,510	154,151
Short-term investments, Gross Unrealized Gains	1	3
Short-term investments, Gross Unrealized Losses	242	405
Short-term investments, Estimated Fair Value	179,269	153,749	[1]
Cash [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	76,134	63,642
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	76,134	63,642
Commercial Paper [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	2,999	6,995
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses		2
Cash and cash equivalents, Fair Value	2,999	6,993
Short-term investments, Amortized Cost	16,649	14,245
Short-term investments, Gross Unrealized Gains		0
Short-term investments, Gross Unrealized Losses	5	8
Short-term investments, Estimated Fair Value	16,644	14,237
Money Market Funds [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	84,802	36,708
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	84,802	36,708
Corporate Debt Obligations [Member]
Schedule of Investments [Line Items]
Short-term investments, Amortized Cost	147,383	110,062
Short-term investments, Gross Unrealized Gains	1	0
Short-term investments, Gross Unrealized Losses	207	347
Short-term investments, Estimated Fair Value	147,177	109,715
US Government Agencies [Member]
Schedule of Investments [Line Items]
Short-term investments, Amortized Cost	14,998	18,998
Short-term investments, Gross Unrealized Gains	0	2
Short-term investments, Gross Unrealized Losses	30	50
Short-term investments, Estimated Fair Value	14,968	18,950
Bank Deposits [Member]
Schedule of Investments [Line Items]
Short-term investments, Amortized Cost	480	10,846
Short-term investments, Gross Unrealized Gains	0	1
Short-term investments, Gross Unrealized Losses	0	0
Short-term investments, Estimated Fair Value	$ 480	$ 10,847

[1] The Condensed Consolidated Balance Sheet as of December 31, 2016 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.