Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	IPO Common stock	IPO Additional paid-in capital	IPO	At The Market Offering Program Common stock	At The Market Offering Program Additional paid-in capital	At The Market Offering Program	Common stock	Additional paid-in capital	Accumulated deficit	Total
Stockholders' (deficit) equity beginning balance at Dec. 31, 2018							$ 333	$ 254,516	$ (105,538)	$ 149,311
Stockholders' (deficit) equity shares beginning balance at Dec. 31, 2018							33,341,000
Stockholders' (Deficit) Equity Rollforward
Issuance of common stock upon vesting of restricted stock							$ 2	(2)
Issuance of common stock upon vesting of restricted stock (in shares)							139,000
Stock-based compensation								4,325		4,325
Issuance of common stock upon exercise of stock options							$ 1	251		252
Issuance of common stock upon exercise of stock options (in shares)							128,000
Net loss									(28,842)	(28,842)
Stockholders' (deficit) equity ending balance at Jun. 30, 2019							$ 336	259,090	(134,380)	125,046
Stockholders' (deficit) equity shares ending balance at Jun. 30, 2019							33,608,000
Stockholders' (deficit) equity beginning balance at Mar. 31, 2019							$ 334	256,601	(122,249)	134,686
Stockholders' (deficit) equity shares beginning balance at Mar. 31, 2019							33,437,000
Stockholders' (Deficit) Equity Rollforward
Issuance of common stock upon vesting of restricted stock							$ 1	(1)
Issuance of common stock upon vesting of restricted stock (in shares)							69,000
Stock-based compensation								2,325		2,325
Issuance of common stock upon exercise of stock options							$ 1	165		166
Issuance of common stock upon exercise of stock options (in shares)							102,000
Net loss									(12,131)	(12,131)
Stockholders' (deficit) equity ending balance at Jun. 30, 2019							$ 336	259,090	(134,380)	125,046
Stockholders' (deficit) equity shares ending balance at Jun. 30, 2019							33,608,000
Stockholders' (deficit) equity beginning balance at Dec. 31, 2019							$ 337	263,922	(162,948)	$ 101,311
Stockholders' (deficit) equity shares beginning balance at Dec. 31, 2019							33,739,000			33,739,000
Stockholders' (Deficit) Equity Rollforward
Issuance of common stock upon vesting of restricted stock (in shares)							23,000
Stock-based compensation								4,834		$ 4,834
Issuance of stock, net of sales commission and other offering costs	$ 117	$ 33,225	$ 33,342	$ 12	$ 4,563	$ 4,575
Issuance of stock, net of sales commission and other offering costs (in shares)	11,692,000			1,193,000
Issuance of common stock upon exercise of stock options							$ 2	471		473
Issuance of common stock upon exercise of stock options (in shares)							203,000
Net loss									(27,227)	(27,227)
Stockholders' (deficit) equity ending balance at Jun. 30, 2020							$ 468	307,015	(190,175)	$ 117,308
Stockholders' (deficit) equity shares ending balance at Jun. 30, 2020							46,850,000			46,850,000
Stockholders' (deficit) equity beginning balance at Mar. 31, 2020							$ 455	299,721	(177,658)	$ 122,518
Stockholders' (deficit) equity shares beginning balance at Mar. 31, 2020							45,546,000
Stockholders' (Deficit) Equity Rollforward
Issuance of common stock upon vesting of restricted stock (in shares)							12,000
Stock-based compensation								2,503		2,503
Issuance of stock, net of sales commission and other offering costs				$ 12	$ 4,563	$ 4,575
Issuance of stock, net of sales commission and other offering costs (in shares)				1,193,000		1,192,549
Issuance of common stock upon exercise of stock options							$ 1	228		229
Issuance of common stock upon exercise of stock options (in shares)							99,000
Net loss									(12,517)	(12,517)
Stockholders' (deficit) equity ending balance at Jun. 30, 2020							$ 468	$ 307,015	$ (190,175)	$ 117,308
Stockholders' (deficit) equity shares ending balance at Jun. 30, 2020							46,850,000			46,850,000