Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 124,004	$ 244	$ 252,012	$ (128,252)
Beginning balance, shares at Dec. 31, 2018		26,747,438
Issuance of common stock under employee stock plans	159		159
Issuance of common stock under employee stock plans, shares		10,606
Forfeiture of common stock underlying incentive units, shares		(5,618)
Equity-based compensation expense	2,925		2,925
Net loss	(28,645)			(28,645)
Ending balance at Mar. 31, 2019	98,443	$ 244	255,096	(156,897)
Ending balance, shares at Mar. 31, 2019		26,752,426
Beginning balance at Dec. 31, 2019	162,300	$ 300	402,077	(240,077)
Beginning balance, shares at Dec. 31, 2019		32,050,906
Issuance of common stock under employee stock plans	521	$ 1	520
Issuance of common stock under employee stock plans, shares		27,532
Forfeiture of common stock underlying incentive units, shares		(2,343)
Equity-based compensation expense	2,586		2,586
Net loss	(30,163)			(30,163)
Ending balance at Mar. 31, 2020	$ 135,244	$ 301	$ 405,183	$ (270,240)
Ending balance, shares at Mar. 31, 2020		32,076,095