Selected Quarterly Financial Data (Schedule Of Selected Quarterly Financial Data) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Data [Abstract]
Revenue
Operating expenses:
General and administrative	$ 3,814	$ 5,675	$ 5,173	$ 5,383	$ 5,801	$ 4,434	$ 3,924	$ 1,344	20,045	15,503	3,415
Research and development	5,080	5,038	3,960	3,175	2,864	2,925	2,130	1,727	17,253	9,646	5,506
Amortization of intangible assets	166	166	167	166	166	166	167	166	665	665	665
Total operating expenses	9,060	10,879	9,300	8,724	8,831	7,525	6,221	3,237	37,963	25,814	9,586
Other income (expense):
Interest income	135	118	137	56	128	39	41	39	446	247	68
Total other income (expense)	107	118	137	56	128	39	41	39	418	247	68
Loss from operations, before income taxes	(8,953)	(10,761)	(9,163)	(8,668)	(8,703)	(7,486)	(6,180)	(3,198)	(37,545)	(25,567)	(9,518)
Income tax benefit
Net loss	(8,953)	(10,761)	(9,163)	(8,668)	(8,703)	(7,486)	(6,180)	(3,198)	(37,545)	(25,567)	(9,518)
Other comprehensive loss:
Unrealized gain (loss) on available-for-sale securities, net of tax	2	(3)	3	48	(49)	4	3	(2)	50	(44)	(7)
Comprehensive loss	$ (8,951)	$ (10,764)	$ (9,160)	$ (8,620)	$ (8,752)	$ (7,482)	$ (6,177)	$ (3,200)	$ (37,495)	$ (25,611)	$ (9,525)
Basic and diluted net loss per share	$ (0.51)	$ (0.64)	$ (0.54)	$ (0.51)	$ (0.53)	$ (0.52)	$ (0.43)	$ (0.23)	$ (2.20)	$ (1.73)	$ (0.86)
Weighted average shares used to compute net loss per common share - basic and diluted	17,656	16,927	16,881	16,842	16,574	14,381	14,233	13,803	17,078	14,754	11,009