CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock Public Offering	Common Stock	Additional Paid-in Capital Public Offering	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Loss	Accumulated Deficit	Public Offering	Total
Balance at Dec. 31, 2017		$ 41		$ 202,790		$ (96)	$ (144,727)		$ 58,008
Balance (in shares) at Dec. 31, 2017		40,549,936			29,231
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense				4,788					4,788
Issuance of stock	$ 12		$ 42,135					$ 42,147
Issuance of stock (in shares)	12,000,000
Exercise of stock options				14					14
Exercise of stock options (in shares)		12,308
Forfeiture of restricted stock (in shares)		(14,000)
Unrealized gain (loss) on investments						94			94
Net loss							(36,726)		(36,726)
Balance at Dec. 31, 2018		$ 53		249,727		(2)	(181,453)		68,325
Balance (in shares) at Dec. 31, 2018		52,548,244			29,231
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense				5,672					5,672
Issuance of common stock under equity distribution agreement, net of expenses of $95		$ 2		2,128					2,130
Issuance of common stock under equity distribution agreement, net of expenses of $95 (in shares)		1,692,289
Issuance of stock	$ 32		$ 37,432					$ 37,464
Issuance of stock (in shares)	32,200,000
Exercise of stock options				97					97
Exercise of stock options (in shares)		80,020
Forfeiture of restricted stock (in shares)		(20,200)
Unrealized gain (loss) on investments						$ 2			2
Net loss							(54,121)		(54,121)
Balance at Dec. 31, 2019		$ 87		$ 295,056			$ (235,574)		$ 59,569
Balance (in shares) at Dec. 31, 2019		86,500,353			29,231