Stock Benefit Plans and Equity Transactions - Summary of Total Stock Based Compensation (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	$ 1,675	$ 450	$ 3,442	$ 1,669
Cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	18	13	51	27
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	179	(52)	192	239
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	223	134	527	358
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	$ 1,255	$ 355	$ 2,672	$ 1,045