Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Direct Offering [Member] Common Stock [Member]	Direct Offering [Member] Additional Paid-in Capital [Member]	Direct Offering [Member] Retained Earnings [Member]	Direct Offering [Member]	At-the-market Offering [Member] Common Stock [Member]	At-the-market Offering [Member] Additional Paid-in Capital [Member]	At-the-market Offering [Member] Retained Earnings [Member]	At-the-market Offering [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balances (in shares) at Dec. 31, 2019									15,001,795
Balances at Dec. 31, 2019									$ 2	$ 539,158	$ (470,111)	$ 69,049
Issuance of common stock upon exercise of options (in shares)									5,645
Issuance of common stock upon exercise of options									$ 0	33	0	33
Stock-based compensation									0	717	0	717
Net loss									$ 0	0	(10,796)	(10,796)
Issuance of common stock under employee benefit plans (in shares)									8,492
Issuance of common stock under employee benefit plans									$ 0	0	0	0
Balances (in shares) at Mar. 31, 2020									15,015,932
Balances at Mar. 31, 2020									$ 2	539,908	(480,907)	59,003
Balances (in shares) at Dec. 31, 2019									15,001,795
Balances at Dec. 31, 2019									$ 2	539,158	(470,111)	69,049
Net loss												(26,497)
Balances (in shares) at Sep. 30, 2020									16,087,266
Balances at Sep. 30, 2020									$ 2	545,972	(496,608)	49,366
Balances (in shares) at Mar. 31, 2020									15,015,932
Balances at Mar. 31, 2020									$ 2	539,908	(480,907)	59,003
Issuance of common stock upon exercise of options (in shares)									13,844
Issuance of common stock upon exercise of options									$ 0	53	0	53
Issuance of common stock (in shares)									931,098
Issuance of common stock									$ 0	4,922	0	4,922
Stock-based compensation									0	488	0	488
Net loss									$ 0	0	(5,041)	(5,041)
Issuance of common stock under employee benefit plans (in shares)									35,303
Issuance of common stock under employee benefit plans									$ 0	22	0	22
Balances (in shares) at Jun. 30, 2020									15,996,177
Balances at Jun. 30, 2020									$ 2	545,393	(485,948)	59,447
Issuance of common stock upon exercise of options (in shares)									91,089
Issuance of common stock									$ 0	203	0	203
Stock-based compensation									0	376	0	376
Net loss									$ 0	0	(10,660)	(10,660)
Balances (in shares) at Sep. 30, 2020									16,087,266
Balances at Sep. 30, 2020									$ 2	545,972	(496,608)	49,366
Balances (in shares) at Dec. 31, 2020									16,481,099
Balances at Dec. 31, 2020									$ 2	548,707	(500,654)	48,055
Issuance of common stock upon exercise of options (in shares)									77,858
Issuance of common stock upon exercise of options									$ 0	260	0	260
Issuance of common stock (in shares)	2,875,000				884,695
Issuance of common stock	$ 0	$ 20,866	$ 0	$ 20,866	$ 0	$ 7,034	$ 0	$ 7,034
Stock-based compensation									0	505	0	505
Net loss									$ 0	0	(8,004)	(8,004)
Balances (in shares) at Mar. 31, 2021									20,318,652
Balances at Mar. 31, 2021									$ 2	577,372	(508,658)	68,716
Balances (in shares) at Dec. 31, 2020									16,481,099
Balances at Dec. 31, 2020									$ 2	548,707	(500,654)	$ 48,055
Issuance of common stock upon exercise of options (in shares)												148,452
Net loss												$ (26,195)
Balances (in shares) at Sep. 30, 2021									20,904,499
Balances at Sep. 30, 2021									$ 2	581,183	(526,849)	54,336
Balances (in shares) at Mar. 31, 2021									20,318,652
Balances at Mar. 31, 2021									$ 2	577,372	(508,658)	68,716
Issuance of common stock upon exercise of options (in shares)									63,094
Issuance of common stock upon exercise of options									$ 0	20	0	20
Issuance of common stock (in shares)					314,983
Issuance of common stock					$ 0	$ 1,816	$ 0	$ 1,816
Stock-based compensation									0	540	0	540
Net loss									$ 0	0	(7,105)	(7,105)
Issuance of common stock under employee benefit plans (in shares)									17,275
Issuance of common stock under employee benefit plans									$ 0	71	0	71
Balances (in shares) at Jun. 30, 2021									20,714,004
Balances at Jun. 30, 2021									$ 2	579,819	(515,763)	64,058
Issuance of common stock upon exercise of options (in shares)									7,500
Issuance of common stock upon exercise of options									$ 0	5	0	5
Issuance of common stock (in shares)									182,995
Issuance of common stock									$ 0	732	0	732
Stock-based compensation									0	627	0	627
Net loss									$ 0	0	(11,086)	(11,086)
Balances (in shares) at Sep. 30, 2021									20,904,499
Balances at Sep. 30, 2021									$ 2	$ 581,183	$ (526,849)	$ 54,336