Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Private Placement [Member]	Common Stock [Member]	Common Stock [Member] Private Placement [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Private Placement [Member]	Accumulated Deficit [Member]
Beginning Balances at Dec. 31, 2018	$ 59,945		$ 1		$ 510,509		$ (450,565)
Beginning Balances, shares at Dec. 31, 2018			11,266,151
Issuance of common stock under employee benefit plans, shares			10,349
Stock-based compensation	1,048				1,048
Cumulative-effect adjustment to equity due to adoption of ASU 2016-02	(1,328)						(1,328)
Net loss	(4,704)						(4,704)
Ending Balances at Mar. 31, 2019	54,961		$ 1		511,557		(456,597)
Ending Balances, shares at Mar. 31, 2019			11,276,500
Beginning Balances at Dec. 31, 2018	59,945		$ 1		510,509		(450,565)
Beginning Balances, shares at Dec. 31, 2018			11,266,151
Net loss	(13,890)
Ending Balances at Sep. 30, 2019	47,530		$ 1		513,312		(465,783)
Ending Balances, shares at Sep. 30, 2019			11,284,964
Beginning Balances at Mar. 31, 2019	54,961		$ 1		511,557		(456,597)
Beginning Balances, shares at Mar. 31, 2019			11,276,500
Issuance of common stock upon exercise of options	2				2
Issuance of common stock upon exercise of options, shares			2,000
Issuance of common stock under employee benefit plans	11				11
Issuance of common stock under employee benefit plans, shares			6,080
Stock-based compensation	941				941
Net loss	(3,044)						(3,044)
Ending Balances at Jun. 30, 2019	52,871		$ 1		512,511		(459,641)
Ending Balances, shares at Jun. 30, 2019			11,284,580
Issuance of common stock under employee benefit plans	1				1
Issuance of common stock under employee benefit plans, shares			384
Stock-based compensation	800				800
Net loss	(6,142)						(6,142)
Ending Balances at Sep. 30, 2019	47,530		$ 1		513,312		(465,783)
Ending Balances, shares at Sep. 30, 2019			11,284,964
Beginning Balances at Dec. 31, 2019	69,049		$ 2		539,158		(470,111)
Beginning Balances, shares at Dec. 31, 2019			15,001,795
Issuance of common stock upon exercise of options	33				33
Issuance of common stock upon exercise of options, shares			5,645
Issuance of common stock under employee benefit plans, shares			8,492
Stock-based compensation	717				717
Net loss	(10,796)						(10,796)
Ending Balances at Mar. 31, 2020	59,003		$ 2		539,908		(480,907)
Ending Balances, shares at Mar. 31, 2020			15,015,932
Beginning Balances at Dec. 31, 2019	$ 69,049		$ 2		539,158		(470,111)
Beginning Balances, shares at Dec. 31, 2019			15,001,795
Issuance of common stock upon exercise of options, shares	110,578
Net loss	$ (26,497)
Ending Balances at Sep. 30, 2020	49,366		$ 2		545,972		(496,608)
Ending Balances, shares at Sep. 30, 2020			16,087,266
Beginning Balances at Mar. 31, 2020	59,003		$ 2		539,908		(480,907)
Beginning Balances, shares at Mar. 31, 2020			15,015,932
Issuance of common stock in private placement, net of issuance costs of $78		$ 4,922				$ 4,922
Issuance of common stock in private placement, net of issuance costs of $78, shares				931,098
Issuance of common stock upon exercise of options	53				53
Issuance of common stock upon exercise of options, shares			13,844
Issuance of common stock under employee benefit plans	22				22
Issuance of common stock under employee benefit plans, shares			35,303
Stock-based compensation	488				488
Net loss	(5,041)						(5,041)
Ending Balances at Jun. 30, 2020	59,447		$ 2		545,393		(485,948)
Ending Balances, shares at Jun. 30, 2020			15,996,177
Issuance of common stock upon exercise of options	203				203
Issuance of common stock upon exercise of options, shares			91,089
Stock-based compensation	376				376
Net loss	(10,660)						(10,660)
Ending Balances at Sep. 30, 2020	$ 49,366		$ 2		$ 545,972		$ (496,608)
Ending Balances, shares at Sep. 30, 2020			16,087,266