Income Taxes - Provision (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income tax expense (benefit)	$ 3,400	$ (1,030)	$ 437	$ (6,860)
Reduction in deferred tax liabilities related to extension of tax rate in china	(500)
Benefit related to stock compensation windfalls	$ 300	400	$ 6,100	$ 4,100
Benefit related to remeasurement of net U.S. deferred tax assets		1,400
Transition tax reduction		$ 1,100