Cash, Cash Equivalents, and Short-Term Investments - Summary of Cash, Cash Equivalents and Short-Term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	$ 107,345	$ 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	107,343	168,252
Short-term investments, Amortized Cost	154,151	96,853
Short-term investments, Gross Unrealized Gains	3	2
Short-term investments, Gross Unrealized Losses	405	300
Short-term investments, Estimated Fair Value	153,749	96,555
Cash [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	63,642	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	63,642	57,906
Commercial Paper [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	6,995	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	6,993	13,893
Short-term investments, Amortized Cost	14,245
Short-term investments, Gross Unrealized Gains	0
Short-term investments, Gross Unrealized Losses	8
Short-term investments, Estimated Fair Value	14,237
Money Market Funds [Member]
Schedule of Investments [Line Items]
Cash and cash equivalents, Amortized Cost	36,708	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	36,708	86,200
Corporate Debt Obligations [Member]
Schedule of Investments [Line Items]
Short-term investments, Amortized Cost	110,062	86,590
Short-term investments, Gross Unrealized Gains	0	2
Short-term investments, Gross Unrealized Losses	347	300
Short-term investments, Estimated Fair Value	109,715	86,292
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	10,846	10,263
Short-term investments, Gross Unrealized Gains	1	0
Short-term investments, Gross Unrealized Losses	0	0
Short-term investments, Estimated Fair Value	10,847	$ 10,263
US Government Agencies [Member]
Schedule of Investments [Line Items]
Short-term investments, Amortized Cost	18,998
Short-term investments, Gross Unrealized Gains	2
Short-term investments, Gross Unrealized Losses	50
Short-term investments, Estimated Fair Value	$ 18,950