Short-Term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 90,974	$ 7,188
Unrealized Gross Gains	0	0
Unrealized Gross Losses	(52)	0
Aggregate Fair Value	90,922	7,188
Investments with maturity greater than one year	0	0
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	27,898	5,384
Unrealized Gross Gains	0	0
Unrealized Gross Losses	0	0
Aggregate Fair Value	27,898	5,384
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	28,043	1,804
Unrealized Gross Gains	0	0
Unrealized Gross Losses	(31)	0
Aggregate Fair Value	28,012	$ 1,804
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,074
Unrealized Gross Gains	0
Unrealized Gross Losses	(19)
Aggregate Fair Value	17,055
U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,959
Unrealized Gross Gains	0
Unrealized Gross Losses	(2)
Aggregate Fair Value	$ 17,957

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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Amortized cost 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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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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