CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 196,355	$ 3	$ 292,187	$ (77)	$ (95,758)
Beginning balance, Shares at Dec. 31, 2018		37,358,526
Vesting of common stock from option exercises	18		18
Vesting of common stock from option exercises, Shares		31,584
Issuance of common stock from option exercises	21		21
Issuance of common stock from option exercises, Shares		18,876
Issuance of common stock pursuant to employee stock purchase plan	$ 396		396
Issuance of common stock pursuant to employee stock purchase plan, Shares	28,311	28,311
Stock-based compensation	$ 1,243		1,243
Other comprehensive gain (loss)	83			83
Net loss	(23,852)				(23,852)
Ending balance at Mar. 31, 2019	174,264	$ 3	293,865	6	(119,610)
Ending balance, Shares at Mar. 31, 2019		37,437,297
Beginning balance at Dec. 31, 2019	258,507	$ 4	457,994	183	(199,674)
Beginning balance, Shares at Dec. 31, 2019		45,116,742
Vesting of common stock from option exercises	12		12
Vesting of common stock from option exercises, Shares		15,542
Issuance of common stock from option exercises	$ 135		135
Issuance of common stock from option exercises, Shares	34,311	34,311
Issuance of common stock pursuant to employee stock purchase plan	$ 537		537
Issuance of common stock pursuant to employee stock purchase plan, Shares		39,471
Stock-based compensation	2,883		2,883
Other comprehensive gain (loss)	(202)			(202)
Net loss	(35,331)				(35,331)
Ending balance at Mar. 31, 2020	$ 226,541	$ 4	$ 461,561	$ (19)	$ (235,005)
Ending balance, Shares at Mar. 31, 2020		45,206,066