Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information [Line Items]
Revenue	$ 13	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 13	$ 0	$ 0
Expenses	1,681	2,994	1,944	1,869	1,463	1,512	1,131	1,379	8,488	5,485	4,542
Loss from operations	(1,668)	(2,994)	(1,944)	(1,869)	(1,463)	(1,512)	(1,131)	(1,379)	(8,475)	(5,485)	(4,542)
Other income	297	1,424	2	2	5	4	5	4	1,725	18	23
Net loss	$ (1,371)	$ (1,570)	$ (1,942)	$ (1,867)	$ (1,458)	$ (1,508)	$ (1,126)	$ (1,375)	$ (6,750)	$ (5,467)	$ (4,519)
Net loss per common share - basic and diluted	$ (0.01)	$ (0.02)	$ (0.02)	$ (0.02)	$ (0.02)	$ (0.02)	$ (0.01)	$ (0.02)	$ (0.07)	$ (0.06)	$ (0.05)