Loss Per Share - Calculation of Basic and Diluted Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net loss	$ (4,400)	$ (3,900)	$ (3,600)	$ (3,800)	$ (2,800)	$ (4,100)	$ (3,300)	$ (4,000)	$ (15,681)	$ (14,232)	$ (11,172)
Dividends related to Series B convertible preferred stock									(588)	(589)	(589)
Net loss available to common stockholders	$ (4,500)	$ (4,100)	$ (3,700)	$ (4,000)	$ (3,000)	$ (4,300)	$ (3,400)	$ (4,100)	$ (16,269)	$ (14,821)	$ (11,761)
Per share of Common Stock
Basic net loss available to common stockholders	$ (0.18)	$ (0.17)	$ (0.17)	$ (0.18)	$ (0.14)	$ (0.21)	$ (0.18)	$ (0.22)	$ (0.70)	$ (0.74)	$ (0.70)
Weighted average shares outstanding (basic and diluted)									23,264	19,923	16,722
Currently anti-dilutive common stock equivalents									2,210	2,020	1,700