Net Loss Per Share - Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net loss available to common stockholders	$ (160)	$ (1,670)	$ (1,952)	$ (2,880)	$ (3,725)	$ (4,314)	$ (3,279)	$ (3,706)	$ (6,661)	$ (15,343)	$ (2,602)
Denominator:
Weighted average shares outstanding - basic	14,281	14,297	13,179	12,163	12,323	12,209	11,741	11,524	13,489	11,951	11,486
Weighted average shares outstanding - diluted	14,281	14,297	13,179	12,163	12,323	12,209	11,741	11,524	13,489	11,951	11,486
Shares excluded (anti-dilutive)											17
Shares excluded due to an exercise price greater than weighted average stock price for the period									1,839	2,094	383
Net loss per common share:
Basic	$ (0.01)	$ (0.12)	$ (0.15)	$ (0.24)	$ (0.30)	$ (0.35)	$ (0.28)	$ (0.32)	$ (0.49)	$ (1.28)	$ (0.23)
Diluted	$ (0.01)	$ (0.12)	$ (0.15)	$ (0.24)	$ (0.30)	$ (0.35)	$ (0.28)	$ (0.32)	$ (0.49)	$ (1.28)	$ (0.23)