Consolidated Statements of Stockholders’ Equity - USD ($) $ in Thousands	Common Stock At-the-market offering	Common Stock	Additional Paid-In Capital At-the-market offering	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	At-the-market offering	Total
Balance, Beginning at Dec. 31, 2016				$ 152,393	$ (245)	$ (64,593)		$ 87,555
Balance, Beginning (in shares) at Dec. 31, 2016		16,722,280
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon public offering, net of issuance costs				64,547				64,547
Issuance of common stock upon public offering, net of issuance costs (in shares)		4,059,500
Issuance of common stock upon under equity incentive and employee stock purchase plans				1,007				1,007
Issuance of common stock upon under equity incentive and employee stock purchase plans (in shares)		306,526
Stock-based compensation expense				4,241				4,241
Other comprehensive gain (loss)					239			239
Net loss						(36,957)		(36,957)
Balance, Ending at Dec. 31, 2017				222,188	(6)	(101,550)		120,632
Balance, Ending (in shares) at Dec. 31, 2017		21,088,306
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon public offering, net of issuance costs			$ 1,508				$ 1,508
Issuance of common stock upon public offering, net of issuance costs (in shares)	151,273
Issuance of common stock and warrants upon private placement, net of issuance costs				21,673				21,673
Issuance of common stock and warrants upon private placement, net of issuance costs (in shares)		2,750,000
Issuance of common stock upon under equity incentive and employee stock purchase plans				934				934
Issuance of common stock upon under equity incentive and employee stock purchase plans (in shares)		197,640
Retirement of common stock in exchange for common stock warrant				(6,670)				(6,670)
Retirement of common stock in exchange for common stock warrant (in shares)		(1,000,000)
Issuance of common stock warrant in exchange for retirement of common stock				6,670				6,670
Stock-based compensation expense				6,919				6,919
Other comprehensive gain (loss)					(227)			(227)
Net loss						(38,924)		(38,924)
Balance, Ending at Dec. 31, 2018				253,222	(233)	(140,474)		$ 112,515
Balance, Ending (in shares) at Dec. 31, 2018		23,187,219						23,187,219
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon public offering, net of issuance costs			$ 34,492				$ 34,492
Issuance of common stock upon public offering, net of issuance costs (in shares)	2,846,641
Issuance of common stock upon under equity incentive and employee stock purchase plans				1,779				$ 1,779
Issuance of common stock upon under equity incentive and employee stock purchase plans (in shares)		583,792
Issuance of common stock upon exercise of Exchange Warrants (in shares)		599,997
Stock-based compensation expense				8,353				8,353
Other comprehensive gain (loss)					12			12
Net loss						(77,187)		(77,187)
Balance, Ending at Dec. 31, 2019				$ 297,846	$ (221)	$ (217,661)		$ 79,964
Balance, Ending (in shares) at Dec. 31, 2019		27,217,649						27,217,649