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Balance Sheet Components - Summary of Cash Equivalents and Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	$ 102,196	$ 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	(51)	(74)
Total cash equivalents and available-for-sale securities, Fair Value	102,145	85,169
Cash equivalents	47,638	18,504
Available-for-sale securities - current	43,191	56,515
Available-for-sale securities - noncurrent	11,316	10,150
Total cash equivalents and available-for-sale securities, Fair Value	102,145	85,169
Corporate Bonds Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	7,502	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	(7)	(45)
Total cash equivalents and available-for-sale securities, Fair Value	7,495	21,841
Total cash equivalents and available-for-sale securities, Fair Value	7,495	21,841
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	47,638	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	47,638	11,270
Total cash equivalents and available-for-sale securities, Fair Value	47,638	11,270
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost		10,769
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains		0
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses		0
Total cash equivalents and available-for-sale securities, Fair Value		10,769
Total cash equivalents and available-for-sale securities, Fair Value		10,769
Government Bonds [Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	47,056	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	(44)	(29)
Total cash equivalents and available-for-sale securities, Fair Value	47,012	41,289
Total cash equivalents and available-for-sale securities, Fair Value	$ 47,012	$ 41,289

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Cash equivalents and available for sale securities amortized cost.

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

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Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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-Topic 320
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-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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