Income Taxes - Provision (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income tax expense (benefit)	$ (7,260)	$ (5,350)	$ (400)	$ 49,831
Benefit related to stock compensation windfalls	400		4,500
Benefit related to remeasurement of net U.S. deferred tax assets			1,400
Benefit related to transition tax reduction	4,300		$ 3,200
Benefit related to reduction of reserves	$ 300	$ 56,300
Benefit related to remeasurement of net U.S. deferred tax liabilities				$ 700
U.S. statutory federal tax rate (as a percent)				21.00%