Statements of Stockholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Common stock	Additional paid-in capital	Accumulated deficit	Total
Stockholders' (deficit) equity beginning balance at Dec. 31, 2017	$ 53	$ 12,486	$ (52,257)	$ (39,718)
Stockholders' (deficit) equity shares beginning balance at Dec. 31, 2017	5,342
Stockholders' (Deficit) Equity Rollforward
Issuance of common stock upon vesting of restricted stock awards	$ 3	(3)
Issuance of common stock upon vesting of restricted stock awards (in shares)	293
Stock-based compensation		3,318		3,318
Conversion of preferred stock upon IPO	$ 203	132,183		132,386
Conversion of preferred stock upon IPO (in shares)	20,306
Issuance of common stock upon IPO, net of underwriters’ discount and other offering costs of $3,012	$ 74	106,431		106,505
Issuance of common stock upon IPO, net of underwriters’ discount and other offering costs of $3,012 (in shares)	7,360
Issuance of common stock upon exercise of stock options		101		101
Issuance of common stock upon exercise of stock options (in shares)	40
Net loss			(53,281)	(53,281)
Stockholders' (deficit) equity ending balance at Dec. 31, 2018	$ 333	254,516	(105,538)	$ 149,311
Stockholders' (deficit) equity shares ending balance at Dec. 31, 2018	33,341			33,341
Stockholders' (Deficit) Equity Rollforward
Issuance of common stock upon vesting of restricted stock awards	$ 2	(2)
Issuance of common stock upon vesting of restricted stock awards (in shares)	217
Stock-based compensation		9,036		$ 9,036
Issuance of common stock upon exercise of stock options	$ 2	372		374
Issuance of common stock upon exercise of stock options (in shares)	181
Net loss			(57,410)	(57,410)
Stockholders' (deficit) equity ending balance at Dec. 31, 2019	$ 337	$ 263,922	$ (162,948)	$ 101,311
Stockholders' (deficit) equity shares ending balance at Dec. 31, 2019	33,739			33,739