Stockholders' Equity - Stock-Based Compensation Expense Related to Stock Options and RSUs (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense included in expenses	$ 1,889	$ 1,085
Cost of revenue
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense included in expenses	18	12
Selling and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense included in expenses	641	347
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense included in expenses	367	208
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense included in expenses	$ 863	$ 518