Reconciliation Between Income Taxes at Statutory Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Effective Income Tax Rate Reconciliation [Line Items]
Loss before income taxes	$ (6,750)	$ (5,467)	$ (4,560)
Tax (benefit) @ statutory tax rate	(2,295)	(1,859)	(1,550)
Effects of:
Exclusion of incentive stock option expense	117	89	83
R&D tax credits	(252)	(132)	(132)
Increase in valuation allowance	3,001	1,899	1,530
FMV of warrants	(582)	0	0
Prior year adjustments	6	0	0
Carryforward adjustment		0	21
Other	5	3	48
Provision for income taxes	$ 0	$ 0	$ 0