Stock Benefit Plans and Equity Transactions - Summary of Total Stock Based Compensation (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	$ 1,148	$ 411	$ 1,767	$ 1,219
Cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	11	11	33	14
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	129	(20)	13	291
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	193	151	304	224
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line items]
Total stock-based compensation	$ 815	$ 269	$ 1,417	$ 690