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, 2017	$ 82,753	$ 1	$ 456,984	$ (374,232)
Beginning Balances, shares at Dec. 31, 2017		5,989,688
Issuance of common stock upon exercise of options	35		35
Issuance of common stock upon exercise of options, shares		3,643
Issuance of common stock under employee benefit plans, shares		18,300
Stock-based compensation	2,820		2,820
Net loss	(8,981)			(8,981)
Ending Balances at Mar. 31, 2018	76,627	$ 1	459,839	(383,213)
Ending Balances, shares at Mar. 31, 2018		6,011,631
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