Balance Sheet Components (Schedule of Available-for-Sale Short-Term Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cost	$ 149	$ 70,479
Unrealized Gains	0	1
Unrealized Losses	0	(17)
Estimated Fair Value	149	70,463
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Cost	0	70,330
Unrealized Gains	0	1
Unrealized Losses	0	(17)
Estimated Fair Value	0	70,314
Certificates of deposits
Debt Securities, Available-for-sale [Line Items]
Cost	149	149
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	$ 149	$ 149

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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-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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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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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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