Balance Sheet Components - Summary of Cash Equivalents and Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	$ 63,438	$ 85,241
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	2
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(75)	(74)
Total cash equivalents and available-for-sale securities, Fair Value	63,363	85,169
Cash equivalents	9,236	18,504
Available-for-sale securities - current	54,127	56,515
Available-for-sale securities - noncurrent	0	10,150
Total cash equivalents and available-for-sale securities, Fair Value	63,363	85,169
Corporate Bonds Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	15,839	21,886
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	0
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(18)	(45)
Total cash equivalents and available-for-sale securities, Fair Value	15,821	21,841
Total cash equivalents and available-for-sale securities, Fair Value	15,821	21,841
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	9,236	11,270
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	0
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	0	0
Total cash equivalents and available-for-sale securities, Fair Value	9,236	11,270
Total cash equivalents and available-for-sale securities, Fair Value	9,236	11,270
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	1,200	10,769
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	0
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	0	0
Total cash equivalents and available-for-sale securities, Fair Value	1,200	10,769
Total cash equivalents and available-for-sale securities, Fair Value	1,200	10,769
Government Bonds [Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	37,163	41,316
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	2
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(57)	(29)
Total cash equivalents and available-for-sale securities, Fair Value	37,106	41,289
Total cash equivalents and available-for-sale securities, Fair Value	$ 37,106	$ 41,289