Balance Sheet Components - Fair Value of Available-For-Sale Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 96,827	$ 104,093
Gross Unrealized Gains	477	9
Gross Unrealized Losses	(35)	(7)
Estimated Fair Value	97,269	104,095
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	23,202	34,363
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	23,202	34,363
U.S. treasury bills
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,997
Gross Unrealized Gains	3
Gross Unrealized Losses	0
Estimated Fair Value	4,000
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,938	9,919
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	9,938	9,919
Corporate bonds/notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,227	10,180
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(30)	(4)
Estimated Fair Value	10,197	10,176
U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	44,280	44,450
Gross Unrealized Gains	474	9
Gross Unrealized Losses	0	(3)
Estimated Fair Value	44,754	44,456
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,183	5,181
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5)	0
Estimated Fair Value	5,178	5,181
Cash equivalents
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	27,202	34,363
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 70,067	51,508
Long-term investments
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value		$ 18,224

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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