Investments - Schedule of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Total	$ 50,300	$ 100,389
Gross Unrealized Gains	62	2
Gross Unrealized Losses	(13)	(173)
Fair Value	50,349	100,218
Certificates of deposit
Investment [Line Items]
Total	6,869	10,787
Gross Unrealized Gains	17	0
Gross Unrealized Losses	(5)	0
Fair Value	6,881	10,787
U.S. Treasury securities
Investment [Line Items]
Total	20,982	22,185
Gross Unrealized Gains	31	1
Gross Unrealized Losses	(2)	(66)
Fair Value	21,011	22,120
U.S. Agency securities
Investment [Line Items]
Total	4,013	8,024
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(5)	(45)
Fair Value	4,008	7,980
Commercial paper
Investment [Line Items]
Total	6,080	17,025
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	6,080	17,025
Asset-backed securities
Investment [Line Items]
Total		12,007
Gross Unrealized Gains		0
Gross Unrealized Losses		(9)
Fair Value		11,998
Corporate notes and bonds
Investment [Line Items]
Total	12,356	30,361
Gross Unrealized Gains	14	0
Gross Unrealized Losses	(1)	(53)
Fair Value	$ 12,369	$ 30,308

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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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