Consolidated Statements of Stockholders' Deficit - 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, 2018	$ 4	333,114	(297,243)	35,875
Balance, shares at Dec. 31, 2018	41,518,091
Stockholders' (Deficit) Equity
Net loss				(41,577)
Balance at Jun. 30, 2019	$ 4	347,074	(338,820)	8,258
Balance, shares at Jun. 30, 2019	44,101,583
Balance at Mar. 31, 2019	$ 4	340,011	(314,367)	25,648
Balance, shares at Mar. 31, 2019	42,836,978
Stockholders' (Deficit) Equity
Issuance of common stock in connection with employee stock purchase plan		294		294
Issuance of common stock in connection with employee stock purchase plan, shares	84,238
Issuance of common stock upon public offering, net of issuance costs		5,074		5,074
Issuance of common stock upon public offering, net of issuance costs, shares	1,180,367
Stock-based compensation expense		1,695		1,695
Net loss			(24,453)	(24,453)
Balance at Jun. 30, 2019	$ 4	347,074	(338,820)	8,258
Balance, shares at Jun. 30, 2019	44,101,583
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 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
Balance at Dec. 31, 2019	$ 5	379,980	(383,615)	(3,630)
Balance, shares at Dec. 31, 2019	50,333,559
Stockholders' (Deficit) Equity
Net loss				(58,080)
Balance at Jun. 30, 2020	$ 6	447,033	(441,695)	5,344
Balance, shares at Jun. 30, 2020	62,953,793
Balance at Mar. 31, 2020	$ 5	394,463	(405,127)	(10,659)
Balance, shares at Mar. 31, 2020	53,037,703
Stockholders' (Deficit) Equity
Issuance of common stock upon exercise of stock options		378		378
Issuance of common stock upon exercise of stock options, shares	75,862
Issuance of common stock in connection with employee stock purchase plan		350		350
Issuance of common stock in connection with employee stock purchase plan, shares	104,579
Issuance of common stock upon public offering, net of issuance costs	$ 1	50,016		50,017
Issuance of common stock upon public offering, net of issuance costs, shares	9,735,649
Stock-based compensation expense		1,826		1,826
Net loss			(36,568)	(36,568)
Balance at Jun. 30, 2020	$ 6	$ 447,033	$ (441,695)	$ 5,344
Balance, shares at Jun. 30, 2020	62,953,793