Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 5,240	$ 4,633	$ 14,537	$ 14,269
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	4,881	4,431	13,764	13,698
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 359	$ 202	$ 773	$ 571