Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - 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 Gain (Loss)	Accumulated Deficit	At-the-market offering	Total
Balance, Beginning at Dec. 31, 2018				$ 253,222	$ (233)	$ (140,474)		$ 112,515
Balance, Beginning (in shares) at Dec. 31, 2018		23,187,219
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon public offering, net of issuance costs			$ 10,543				$ 10,543
Issuance of common stock upon public offering, net of issuance costs (in shares)	921,684
Issuance of common stock upon under equity incentive and employee stock purchase plans				477				477
Issuance of common stock upon under equity incentive and employee stock purchase plans (in shares)		258,703
Issuance of common stock upon exercise of Exchange Warrants (in shares)		599,997
Stock-based compensation expense				3,992				3,992
Other comprehensive gain (loss)					66			66
Net loss						(43,277)		(43,277)
Balance, Ending at Jun. 30, 2019				268,234	(167)	(183,751)		84,316
Balance, Ending (in shares) at Jun. 30, 2019		24,967,603
Balance, Beginning at Mar. 31, 2019				255,591	(189)	(154,577)		100,825
Balance, Beginning (in shares) at Mar. 31, 2019		23,392,534
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon public offering, net of issuance costs			10,543				10,543
Issuance of common stock upon public offering, net of issuance costs (in shares)	921,684
Issuance of common stock upon under equity incentive and employee stock purchase plans				87				87
Issuance of common stock upon under equity incentive and employee stock purchase plans (in shares)		53,388
Issuance of common stock upon exercise of Exchange Warrants (in shares)		599,997
Stock-based compensation expense				2,013				2,013
Other comprehensive gain (loss)					22			22
Net loss						(29,174)		(29,174)
Balance, Ending at Jun. 30, 2019				268,234	(167)	(183,751)		84,316
Balance, Ending (in shares) at Jun. 30, 2019		24,967,603
Balance, Beginning at Dec. 31, 2019				297,846	(221)	(217,661)		$ 79,964
Balance, Beginning (in shares) at Dec. 31, 2019		27,217,649						27,217,649
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon public offering, net of issuance costs			16,643	105,331			16,643	$ 105,331
Issuance of common stock upon public offering, net of issuance costs (in shares)	1,232,793	8,050,000
Issuance of common stock upon under equity incentive and employee stock purchase plans				991				991
Issuance of common stock upon under equity incentive and employee stock purchase plans (in shares)		301,697
Stock-based compensation expense				4,044				4,044
Other comprehensive gain (loss)					13			13
Net loss						(39,501)		(39,501)
Balance, Ending at Jun. 30, 2020				424,855	(208)	(257,162)		$ 167,485
Balance, Ending (in shares) at Jun. 30, 2020		36,802,139						36,802,139
Balance, Beginning at Mar. 31, 2020				300,300	107	(237,741)		$ 62,666
Balance, Beginning (in shares) at Mar. 31, 2020		27,434,705
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon public offering, net of issuance costs			$ 16,643	105,331			$ 16,643	105,331
Issuance of common stock upon public offering, net of issuance costs (in shares)	1,232,793	8,050,000
Issuance of common stock upon under equity incentive and employee stock purchase plans				585				585
Issuance of common stock upon under equity incentive and employee stock purchase plans (in shares)		84,641
Stock-based compensation expense				1,996				1,996
Other comprehensive gain (loss)					(315)			(315)
Net loss						(19,421)		(19,421)
Balance, Ending at Jun. 30, 2020				$ 424,855	$ (208)	$ (257,162)		$ 167,485
Balance, Ending (in shares) at Jun. 30, 2020		36,802,139						36,802,139