Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member] The March 2020 Offering [Member] Underwriters' Designees [Member]	Common Stock [Member] The March 2020 Offering [Member]	Common Stock [Member] The September 2019 Offering [Member] Underwriters' Designees [Member]	Common Stock [Member] The September 2019 Offering [Member]	Common Stock [Member] The July 2020 Offering [Member]	Common Stock [Member] The April 2019 Offering [Member] Underwriters' Designees [Member]	Common Stock [Member] The April 2019 Offering [Member]	Common Stock [Member] The December 2020 Offering [Member]	Common Stock [Member] The October 2020 Offering [Member] Underwriters' Designees [Member]	Common Stock [Member] Placement Agents' Designees [Member]	Common Stock [Member]	Additional Paid-in Capital [Member] The March 2020 Offering [Member] Underwriters' Designees [Member]	Additional Paid-in Capital [Member] The March 2020 Offering [Member]	Additional Paid-in Capital [Member] The September 2019 Offering [Member] Underwriters' Designees [Member]	Additional Paid-in Capital [Member] The September 2019 Offering [Member]	Additional Paid-in Capital [Member] The July 2020 Offering [Member]	Additional Paid-in Capital [Member] The April 2019 Offering [Member] Underwriters' Designees [Member]	Additional Paid-in Capital [Member] The April 2019 Offering [Member]	Additional Paid-in Capital [Member] The December 2020 Offering [Member]	Additional Paid-in Capital [Member] The October 2020 Offering [Member] Underwriters' Designees [Member]	Additional Paid-in Capital [Member] Placement Agents' Designees [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member] The March 2020 Offering [Member] Underwriters' Designees [Member]	Retained Earnings [Member] The March 2020 Offering [Member]	Retained Earnings [Member] The September 2019 Offering [Member] Underwriters' Designees [Member]	Retained Earnings [Member] The September 2019 Offering [Member]	Retained Earnings [Member] The July 2020 Offering [Member]	Retained Earnings [Member] The April 2019 Offering [Member] Underwriters' Designees [Member]	Retained Earnings [Member] The April 2019 Offering [Member]	Retained Earnings [Member] The December 2020 Offering [Member]	Retained Earnings [Member] The October 2020 Offering [Member] Underwriters' Designees [Member]	Retained Earnings [Member] Placement Agents' Designees [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member] The March 2020 Offering [Member] Underwriters' Designees [Member]	AOCI Attributable to Parent [Member] The March 2020 Offering [Member]	AOCI Attributable to Parent [Member] The July 2020 Offering [Member]	AOCI Attributable to Parent [Member] The December 2020 Offering [Member]	AOCI Attributable to Parent [Member] The October 2020 Offering [Member] Underwriters' Designees [Member]	AOCI Attributable to Parent [Member]	The March 2020 Offering [Member] Underwriters' Designees [Member]	The March 2020 Offering [Member]	The September 2019 Offering [Member] Underwriters' Designees [Member]	The September 2019 Offering [Member]	The July 2020 Offering [Member]	The April 2019 Offering [Member] Underwriters' Designees [Member]	The April 2019 Offering [Member]	The December 2020 Offering [Member]	The October 2020 Offering [Member] Underwriters' Designees [Member]	The October 2020 Offering [Member]	Placement Agents' Designees [Member]	Total
Balances (in shares) at Dec. 31, 2018											7,141,189
Balances at Dec. 31, 2018											$ 1											$ 109,226											$ (98,016)																		$ 11,211
Issuance of common stock, net of offering costs (in shares)											1,200,000
Issuance of common stock, net of offering costs											$ 0											2,440											0																		2,440
Issuance of common stock warrants to placement agents’ designees			$ 0			$ 0				$ 0				$ 333			$ 497				$ 100				$ 0			$ 0				$ 0										$ 333			$ 497					$ 100
Issuance of common stock, pre-funded warrants and common stock warrants, net of offering costs (in shares)				925,455			26,124,828
Issuance of common stock, pre-funded warrants and common stock warrants, net of offering costs				$ 0			$ 3								$ 7,741			$ 7,239								$ 0			$ 0														$ 7,741			$ 7,242
Issuance of common stock upon exercise of pre-funded warrants (in shares)											12,265,455
Issuance of common stock upon exercise of pre-funded warrants											$ 1											1,225											0																		1,226
Issuance of common stock upon exercise of common stock warrants (in shares)											598,067
Issuance of common stock upon exercise of common stock warrants											$ 0											180											0																		180
Stock-based compensation											0											627											0																		627
Net loss											$ 0											0											(18,645)																		$ (18,645)
Issuance of common stock upon exercise of options (in shares)																																																			0
Balances (in shares) at Dec. 31, 2019											48,254,994
Balances at Dec. 31, 2019											$ 5											129,608											(116,661)						$ 0												$ 12,952
Issuance of common stock, net of offering costs (in shares)					12,503,806			692,651
Issuance of common stock, net of offering costs					$ 1			$ 0								$ 97,033			$ 4,900								$ 0			$ 0						$ 0	$ 0							$ 97,034			$ 4,900
Issuance of common stock warrants to placement agents’ designees	$ 0											$ 453											$ 0											$ 0						$ 453
Issuance of common stock, pre-funded warrants and common stock warrants, net of offering costs (in shares)		4,000,000
Issuance of common stock, pre-funded warrants and common stock warrants, net of offering costs		$ 0											$ 8,722											$ 0											$ 0						$ 8,722
Issuance of common stock upon exercise of common stock warrants (in shares)											44,404,966
Issuance of common stock upon exercise of common stock warrants											$ 5											25,946											0						0												25,951
Stock-based compensation											0											4,358											0						0												4,358
Net loss											$ 0											0											(32,220)						0												$ (32,220)
Issuance of common stock upon exercise of options (in shares)											414,676																																								414,676
Issuance of common stock upon exercise of options											$ 0											602											0						0												$ 602
Disgorgement of short-swing profits, net of costs											$ 0											652											0						0												652
Balances (in shares) at Dec. 31, 2020											110,271,093
Balances at Dec. 31, 2020											$ 11											272,274											(148,881)						0												123,404
Issuance of common stock, net of offering costs (in shares)									13,239,839																																								13,239,839
Issuance of common stock, net of offering costs									$ 2											$ 122,208											$ 0							$ 0										$ 122,210
Issuance of common stock upon exercise of pre-funded warrants (in shares)											1,070,921
Issuance of common stock upon exercise of pre-funded warrants											$ 0											1,745											0						0												1,745
Issuance of common stock upon exercise of common stock warrants (in shares)											1,012,540
Issuance of common stock upon exercise of common stock warrants											$ 0											1,849											0						0												1,849
Stock-based compensation											0											8,867											0						0												8,867
Net loss											0											0											(70,470)						0												$ (70,470)
Issuance of common stock upon exercise of options (in shares)																																																			1,070,921
Unrealized losses on available-for-sale investments											$ 0											0											0						(74)												$ (74)
Balances (in shares) at Dec. 31, 2021											125,594,393
Balances at Dec. 31, 2021											$ 13											$ 406,943											$ (219,351)						$ (74)												$ 187,531