Quarterly Financial Data - Summarized Quarterly Information (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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 5,732	$ 5,804	$ 5,862	$ 5,576	$ 7,084	$ 6,478	$ 7,459	$ 7,214	$ 22,974	$ 28,235	$ 39,507
Gross profit	4,377	4,645	4,577	4,293	5,343	4,680	5,547	5,101	17,892	20,671	31,355
Operating loss	(535)	(942)	(1,619)	(2,578)	(3,762)	(4,557)	(3,907)	(3,679)	(5,674)	(15,905)	(2,538)
Net loss	$ (160)	$ (1,670)	$ (1,952)	$ (2,880)	$ (3,725)	$ (4,314)	$ (3,279)	$ (3,706)	$ (6,661)	$ (15,343)	$ (2,602)
Net loss per share - basic	$ (0.01)	$ (0.12)	$ (0.15)	$ (0.24)	$ (0.30)	$ (0.35)	$ (0.28)	$ (0.32)	$ (0.49)	$ (1.28)	$ (0.23)
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
Net loss per share - diluted	$ (0.01)	$ (0.12)	$ (0.15)	$ (0.24)	$ (0.30)	$ (0.35)	$ (0.28)	$ (0.32)	$ (0.49)	$ (1.28)	$ (0.23)
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