Revision of Prior Period Financial Statements - Schedule of Revised Consolidated Statements of Shareholder's Equity (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net change in unrealized gains on available-for-sale securities									$ 98	$ 49	$ (56)
Total stockholders’ equity	$ 135,409				$ 52,137				135,409	52,137	79,341	$ 93,041
Net loss	(17,300)	$ (18,293)	$ (10,725)	$ (8,250)	(16,270)	$ (9,727)	$ (13,304)	$ (11,077)	(54,568)	(50,378)	(29,740)
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net change in unrealized gains on available-for-sale securities										24
Total stockholders’ equity					54,422					54,422	79,553
Net loss			(11,467)	(8,019)	(14,713)		(12,206)	(11,117)		(48,280)	(29,420)
Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net change in unrealized gains on available-for-sale securities										25
Total stockholders’ equity					(2,285)					(2,285)	(212)
Net loss			$ 742	$ (231)	(1,557)		$ (1,098)	$ 40		(2,098)	(320)
Accumulated Other Comprehensive Income (Loss)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net change in unrealized gains on available-for-sale securities									98	49	(56)
Total stockholders’ equity	82				(16)				82	(16)	(65)	(9)
Accumulated Other Comprehensive Income (Loss) | As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net change in unrealized gains on available-for-sale securities										24
Total stockholders’ equity					(41)					(41)
Accumulated Other Comprehensive Income (Loss) | Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net change in unrealized gains on available-for-sale securities										25
Total stockholders’ equity					25					25
Accumulated Deficit
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total stockholders’ equity	$ (260,393)				(205,825)				(260,393)	(205,825)	(156,801)	(127,061)
Net loss									$ (54,568)	(50,378)	(29,740)
Accumulated Deficit | As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total stockholders’ equity					(203,515)					(203,515)	(156,589)	(127,169)
Net loss										(48,280)	(29,420)
Accumulated Deficit | Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total stockholders’ equity					$ (2,310)					(2,310)	(212)	$ 108
Net loss										$ (2,098)	$ (320)