Quarterly Data (Unaudited) - Summary of Quarterly Data (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 Disclosure [Abstract]
Total revenue	$ 12,600	$ 10,400	$ 9,100	$ 10,000	$ 10,400	$ 10,500	$ 9,700	$ 9,300	$ 42,097	$ 39,912	$ 30,319
Gross margin	8,600	7,000	5,900	6,800	7,500	8,000	7,000	6,700	28,300	29,200
Operating loss	(2,200)	(5,000)	(6,000)	(5,600)	(4,200)	(3,800)	(3,400)	(3,700)	(18,814)	(15,056)	(12,995)
Loss before income taxes	(3,100)	(5,800)	(6,200)	(5,800)	(4,300)	(3,900)	(3,600)	(3,800)	(20,927)	(15,643)	(14,209)
Net loss available to common stockholders	$ (3,300)	$ (6,000)	$ (6,300)	$ (6,000)	$ (4,500)	$ (4,100)	$ (3,700)	$ (4,000)	$ (21,563)	$ (16,269)	$ (14,821)
Per share of common stock:
Basic net loss available to common stock holders	$ (0.13)	$ (0.24)	$ (0.25)	$ (0.24)	$ (0.18)	$ (0.17)	$ (0.17)	$ (0.18)	$ (0.86)	$ (0.70)	$ (0.74)
Diluted net loss available to common stock holders	$ (0.13)	$ (0.24)	$ (0.25)	$ (0.24)	$ (0.18)	$ (0.17)	$ (0.17)	$ (0.18)	$ (0.86)	$ (0.70)	$ (0.74)