Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2018	$ 169,860	$ 2	$ 302,393	$ (128)	$ (132,407)
Balance, Shares at Dec. 31, 2018		23,865,451
Stock-based compensation expense	2,205		2,205
Exercise of stock options and vesting of early exercise shares	7		7
Exercise of stock options and vesting of early exercise shares, Shares		1,230
Unrealized gain on available-for-sale securities	149			149
Cumulative-effect adjustment from adoption of ASC 606 accounting standard on revenue recognition | ASC 606	456				456
Net loss	(13,687)				(13,687)
Balance at Mar. 31, 2019	158,990	$ 2	304,605	21	(145,638)
Balance, Shares at Mar. 31, 2019		23,866,681
Balance at Dec. 31, 2019	$ 358,978	$ 3	544,709	9	(185,743)
Balance, Shares at Dec. 31, 2019	32,950,836	32,950,836
Stock-based compensation expense	$ 4,389		4,389
Exercise of stock options and vesting of early exercise shares	524		524
Exercise of stock options and vesting of early exercise shares, Shares		75,989
Unrealized gain on available-for-sale securities	56			56
Net loss	(32,499)				(32,499)
Balance at Mar. 31, 2020	$ 331,448	$ 3	$ 549,622	$ 65	$ (218,242)
Balance, Shares at Mar. 31, 2020	33,026,825	33,026,825