Income Taxes - Provision (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income tax expense (benefit)	$ 5,120	$ 7,260	$ 5,557	$ 400
Expense related to transition tax		4,300		3,200
Benefit related to stock compensation windfalls		400	6,100	$ 4,500
Benefit from a reduction of deferred tax liabilities related to the extension of a tax rate incentive in China			$ 500
Benefit related to remeasurement of net U.S. deferred tax assets		1,400
Benefit related to reduction of reserves		$ 300