Investments - Schedule of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Total	$ 28,920	$ 100,389
Gross Unrealized Gains	59	2
Gross Unrealized Losses	(1)	(173)
Fair Value	28,978	100,218
Certificates of deposit
Investment [Line Items]
Total	4,163	10,787
Gross Unrealized Gains	21	0
Gross Unrealized Losses	(1)	0
Fair Value	4,183	10,787
U.S. Treasury securities
Investment [Line Items]
Total	11,975	22,185
Gross Unrealized Gains	26	1
Gross Unrealized Losses	0	(66)
Fair Value	12,001	22,120
U.S. Agency securities
Investment [Line Items]
Total	1,505	8,024
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	(45)
Fair Value	1,505	7,980
Commercial paper
Investment [Line Items]
Total		17,025
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		17,025
Asset-backed securities
Investment [Line Items]
Total	1,107	12,007
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(9)
Fair Value	1,107	11,998
Corporate notes and bonds
Investment [Line Items]
Total	10,170	30,361
Gross Unrealized Gains	12	0
Gross Unrealized Losses	0	(53)
Fair Value	$ 10,182	$ 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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