Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Preferred Stock [Member]	Common Stock [Member] The September 2019 Offering [Member] Underwriters' Designees [Member]	Common Stock [Member] The September 2019 Offering [Member]	Common Stock [Member] The April 2019 Offering [Member] Underwriters' Designees [Member]	Common Stock [Member] The April 2019 Offering [Member]	Common Stock [Member] Placement Agents' Designees [Member]	Common Stock [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 April 2019 Offering [Member] Underwriters' Designees [Member]	Additional Paid-in Capital [Member] The April 2019 Offering [Member]	Additional Paid-in Capital [Member] Placement Agents' Designees [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member] The September 2019 Offering [Member] Underwriters' Designees [Member]	Retained Earnings [Member] The September 2019 Offering [Member]	Retained Earnings [Member] The April 2019 Offering [Member] Underwriters' Designees [Member]	Retained Earnings [Member] The April 2019 Offering [Member]	Retained Earnings [Member] Placement Agents' Designees [Member]	Retained Earnings [Member]	The September 2019 Offering [Member] Underwriters' Designees [Member]	The September 2019 Offering [Member]	The April 2019 Offering [Member] Underwriters' Designees [Member]	The April 2019 Offering [Member]	Placement Agents' Designees [Member]	Total
Balances (in shares) at Dec. 31, 2017	1,221,064						138,492
Balances at Dec. 31, 2017	$ 1												$ 41,259						$ (79,982)						$ (38,722)
Issuance of common stock warrants													70												70
Stock-based compensation													387												387
Net loss																			(13,105)						(13,105)
Issuance of common stock upon conversion of convertible promissory notes, related parties (in shares)							1,571,702
Issuance of common stock upon conversion of convertible promissory notes, related parties							$ 157						35,420												35,577
Issuance of common stock upon conversion of convertible preferred stock (in shares)	(1,221,064)						1,918,543
Issuance of common stock upon conversion of convertible preferred stock	$ (1)						$ 192						(191)
Reclassification of warrant to equity													70												70
Issuance of common stock upon reverse merger (in shares)							3,510,439
Issuance of common stock upon reverse merger							$ 365						31,403												31,768
Issuance of common stock upon exercise of stock options (in shares)							2,013
Issuance of common stock upon exercise of stock options													13												13
Balances (in shares) at Sep. 30, 2018							7,141,189
Balances at Sep. 30, 2018							$ 714						108,361						(93,087)						15,988
Balances (in shares) at Jun. 30, 2018							7,141,189
Balances at Jun. 30, 2018							$ 714						108,178						(86,539)						22,353
Stock-based compensation													183												183
Net loss																			(6,548)						(6,548)
Balances (in shares) at Sep. 30, 2018							7,141,189
Balances at Sep. 30, 2018							$ 714						108,361						(93,087)						15,988
Balances (in shares) at Dec. 31, 2018							7,141,189
Balances at Dec. 31, 2018							$ 714						108,513						(97,989)						11,238
Issuance of common stock and warrants, net of offering costs (in shares)			26,124,828		925,455
Issuance of common stock and warrants, net of offering costs			$ 2,612		$ 93				$ 4,632		$ 7,648										$ 7,244		$ 7,741
Issuance of common stock warrants								$ 497		$ 333		$ 100								$ 497		$ 333		$ 100
Issuance of common stock upon exercise of pre-funded warrants (in shares)							10,832,122
Issuance of common stock upon exercise of pre-funded warrants							$ 1,083																		1,083
Stock-based compensation													490												490
Net loss																			(12,236)						(12,236)
Cumulative effect of adoption of new leases standard at Dec. 31, 2018																			(27)						(27)
Balances as of January 1, 2019, as adjusted at Dec. 31, 2018							$ 714						108,513						(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							$ 120						2,320												2,440
Reclassification of warrant to equity								$ 497		$ 333		$ 100								$ 497		$ 333		$ 100
Balances (in shares) at Sep. 30, 2019							46,223,594
Balances at Sep. 30, 2019							$ 4,622						124,533						(110,252)						18,903
Balances (in shares) at Jun. 30, 2019							15,785,735
Balances at Jun. 30, 2019							$ 1,579						119,258						(104,992)						15,845
Issuance of common stock and warrants, net of offering costs (in shares)			26,124,828
Issuance of common stock and warrants, net of offering costs			$ 2,612						4,632												7,244
Issuance of common stock warrants									497												497
Issuance of common stock upon exercise of pre-funded warrants (in shares)							4,313,031
Issuance of common stock upon exercise of pre-funded warrants							$ 431																		431
Stock-based compensation													146												146
Net loss																			(5,260)						(5,260)
Reclassification of warrant to equity									$ 497												$ 497
Balances (in shares) at Sep. 30, 2019							46,223,594
Balances at Sep. 30, 2019							$ 4,622						$ 124,533						$ (110,252)						$ 18,903