Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning Balances at Dec. 31, 2017	$ 82,756	$ 1	$ 456,987	$ (374,232)
Beginning Balances, shares at Dec. 31, 2017		5,989,688
Issuance of common stock upon exercise of options	$ 35		35
Issuance of common stock upon exercise of options, shares	3,643	3,643
Issuance of common stock under employee benefit plans	$ 17		17
Issuance of common stock under employee benefit plans, shares		130,905
Stock-based compensation	16,139		16,139
Issuance of common stock for the merger transaction	37,331		37,331
Issuance of common stock for the merger transaction, shares		5,141,915
Net loss	(76,333)			(76,333)
Ending Balances at Dec. 31, 2018	59,945	$ 1	510,509	(450,565)
Ending Balances, shares at Dec. 31, 2018		11,266,151
Issuance of common stock in public offering, net of issuance costs of $351	25,128	$ 1	25,127
Issuance of common stock in public offering, net of issuance costs of $351, shares		3,633,334
Cumulative-effect adjustment to equity due to adoption of ASU 2016-02	(1,328)			(1,328)
Issuance of common stock upon exercise of options	$ 95		95
Issuance of common stock upon exercise of options, shares	39,686	39,686
Issuance of common stock under employee benefit plans	$ 28		28
Issuance of common stock under employee benefit plans, shares		62,624
Stock-based compensation	3,399		3,399
Net loss	(18,218)			(18,218)
Ending Balances at Dec. 31, 2019	$ 69,049	$ 2	$ 539,158	$ (470,111)
Ending Balances, shares at Dec. 31, 2019		15,001,795