Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [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 toadoption 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, 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	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