CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($)	Follow-on Public Offering, One Common Stock	Follow-on Public Offering, One Additional Paid-in Capital	Follow-on Public Offering, One	Series A Convertible Preferred Stock Preferred Stock	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Balance at Dec. 31, 2019					$ 22,000	$ 295,121,000			$ (235,574,000)	$ 59,569,000
Balance (in shares) at Dec. 31, 2019					21,625,088		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense						1,876,000				1,876,000
Exercise of stock options						312,000				312,000
Exercise of stock options (in shares)					59,978
Issuance of restricted stock (in shares)					5,250
Deemed dividend on beneficial conversion feature - Series A convertible preferred stock						8,880,000			(8,880,000)
Unrealized gain (loss) on investments								$ 27,000		27,000
Net loss									(18,672,000)	(18,672,000)
Balance at Mar. 31, 2020					$ 22,000	306,189,000		27,000	(263,126,000)	43,112,000
Balance (in shares) at Mar. 31, 2020					21,690,316		7,307
Balance at Dec. 31, 2019					$ 22,000	295,121,000			(235,574,000)	59,569,000
Balance (in shares) at Dec. 31, 2019					21,625,088		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Net loss										(50,006,000)
Balance at Sep. 30, 2020				$ 8,698,000	$ 31,000	373,143,000		11,000	(294,461,000)	87,423,000
Balance (in shares) at Sep. 30, 2020				9,253	30,582,625		7,307
Balance at Mar. 31, 2020					$ 22,000	306,189,000		27,000	(263,126,000)	43,112,000
Balance (in shares) at Mar. 31, 2020					21,690,316		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense						1,796,000				1,796,000
Exercise of stock options						200,000				200,000
Exercise of stock options (in shares)					47,455
Issuance of common stock	$ 5,000	$ 42,905,000	$ 42,910,000
Issuance of common stock (in shares)	4,600,000
Issuance of common stock under equity distribution agreement						602,000				602,000
Issuance of common stock under equity distribution agreement (in shares)					78,807
Transfer of convertible preferred stock into permanent equity				$ 8,745,000						8,745,000
Transfer of convertible preferred stock into permanent equity (in shares)				9,303
Conversion of convertible preferred stock to common stock					$ 4,000	19,451,000				19,455,000
Conversion of convertible preferred stock to common stock (in shares)					4,139,400
Net loss									(15,675,000)	(15,675,000)
Balance at Jun. 30, 2020				$ 8,745,000	$ 31,000	371,143,000		27,000	(278,801,000)	101,145,000
Balance (in shares) at Jun. 30, 2020				9,303	30,555,978		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense						1,849,000				1,849,000
Exercise of stock options						104,000				104,000
Exercise of stock options (in shares)					16,647
Conversion of convertible preferred stock to common stock				$ (47,000)		47,000
Conversion of convertible preferred stock to common stock (in shares)				(50)	10,000
Unrealized gain (loss) on investments								(16,000)		(16,000)
Net loss									(15,659,000)	(15,659,000)
Balance at Sep. 30, 2020				$ 8,698,000	$ 31,000	373,143,000		$ 11,000	(294,461,000)	87,423,000
Balance (in shares) at Sep. 30, 2020				9,253	30,582,625		7,307
Balance at Dec. 31, 2020				$ 4,469,000	$ 37,000	444,622,000			(311,929,000)	137,199,000
Balance (in shares) at Dec. 31, 2020				4,753	36,585,767		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense						5,035,000				5,035,000
Exercise of stock options						244,000				244,000
Exercise of stock options (in shares)					55,030
Financing costs						(3,000)				(3,000)
Net loss									(27,141,000)	(27,141,000)
Balance at Mar. 31, 2021				$ 4,469,000	$ 37,000	449,898,000			(339,070,000)	115,334,000
Balance (in shares) at Mar. 31, 2021				4,753	36,640,797		7,307
Balance at Dec. 31, 2020				$ 4,469,000	$ 37,000	444,622,000			(311,929,000)	137,199,000
Balance (in shares) at Dec. 31, 2020				4,753	36,585,767		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Net loss										(70,471,000)
Balance at Sep. 30, 2021				$ 4,302,000	$ 37,000	456,555,000			(382,400,000)	78,494,000
Balance (in shares) at Sep. 30, 2021				4,575	36,758,508		7,307
Balance at Mar. 31, 2021				$ 4,469,000	$ 37,000	449,898,000			(339,070,000)	115,334,000
Balance (in shares) at Mar. 31, 2021				4,753	36,640,797		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense						2,991,000				2,991,000
Exercise of stock options						557,000				557,000
Exercise of stock options (in shares)					63,312
Conversion of convertible preferred stock to common stock				$ (167,000)		167,000
Conversion of convertible preferred stock to common stock (in shares)				(178)	35,600
Net loss									(23,823,000)	(23,823,000)
Balance at Jun. 30, 2021				$ 4,302,000	$ 37,000	453,613,000			(362,893,000)	95,059,000
Balance (in shares) at Jun. 30, 2021				4,575	36,739,709		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense						2,841,000				2,841,000
Exercise of stock options					$ 18,799	101,000				101,000
Net loss									(19,507,000)	(19,507,000)
Balance at Sep. 30, 2021				$ 4,302,000	$ 37,000	$ 456,555,000			$ (382,400,000)	$ 78,494,000
Balance (in shares) at Sep. 30, 2021				4,575	36,758,508		7,307