Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2018	$ 4	$ 333,114	$ (297,243)	$ 35,875
Balance, shares at Dec. 31, 2018	41,518,091
Stockholders' (Deficit) Equity
Issuance of common stock upon exercise of stock options		1		1
Issuance of common stock upon exercise of stock options, shares	406
Issuance of common stock upon public offering, net of issuance costs		4,954		4,954
Issuance of common stock upon public offering, net of issuance costs, shares	1,318,481
Stock-based compensation expense		1,942		1,942
Net loss			(17,124)	(17,124)
Balance at Mar. 31, 2019	$ 4	340,011	(314,367)	25,648
Balance, shares at Mar. 31, 2019	42,836,978
Balance at Dec. 31, 2019	$ 5	379,980	(383,615)	(3,630)
Balance, shares at Dec. 31, 2019	50,333,559
Stockholders' (Deficit) Equity
Issuance of common stock upon exercise of stock options		128		$ 128
Issuance of common stock upon exercise of stock options, shares	46,321
Issuance of common stock in connection with employee stock purchase plan, shares				0
Issuance of common stock upon public offering, net of issuance costs		12,690		$ 12,690
Issuance of common stock upon public offering, net of issuance costs, shares	2,657,823
Stock-based compensation expense		1,665		1,665
Net loss			(21,512)	(21,512)
Balance at Mar. 31, 2020	$ 5	$ 394,463	$ (405,127)	$ (10,659)
Balance, shares at Mar. 31, 2020	53,037,703