Balance Sheet Components - Gains and Losses of Marketable Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 142,165	$ 115,683
Gross Unrealized Gains	36	41
Gross Unrealized Losses	(133)	(207)
Fair Value	142,068	115,517
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,198	4,237
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(3)	0
Fair Value	24,196	4,238
U.S. Treasury
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,003	4,996
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6)	0
Fair Value	8,997	4,996
U.S. agency and government sponsored securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,850	8,803
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(13)	(12)
Fair Value	6,837	8,794
U.S. states and municipalities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,263	27,429
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(7)	(75)
Fair Value	8,256	27,355
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	93,851	69,009
Gross Unrealized Gains	35	36
Gross Unrealized Losses	(104)	(120)
Fair Value	$ 93,782	68,925
Non-U.S. government debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,209
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		$ 1,209

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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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=65884222&loc=d3e22054-111558

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-Name Accounting Standards Codification
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-Section 45
-Paragraph 2
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