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, 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
Numerator:
Net loss									$ (2,740)	$ (6,661)
Dividends paid to preferred stockholders									(404)
Net loss available to common stockholders									$ (3,144)	$ (6,661)
Denominator:
Weighted average shares outstanding - basic	26,925	25,020	21,888	15,299	14,281	14,297	13,179	12,163	22,322	13,489
Weighted average shares outstanding - diluted	27,395	25,020	21,888	15,299	14,281	14,297	13,179	12,163	22,322	13,489
Shares excluded due to an exercise price greater than weighted average stock price for the period									1,081	1,839
Net loss per common share:
Basic	$ 0.10	$ (0.04)	$ (0.10)	$ (0.16)	$ (0.01)	$ (0.12)	$ (0.15)	$ (0.24)	$ (0.14)	$ (0.49)
Diluted	$ 0.10	$ (0.04)	$ (0.10)	$ (0.16)	$ (0.01)	$ (0.12)	$ (0.15)	$ (0.24)	$ (0.14)	$ (0.49)