Income Taxes - Provision (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income tax expense (benefit)	$ 4,770	$ (2,963)
Benefit related to stock compensation windfalls	$ 2,500	5,800
Benefit from a reduction of deferred tax liabilities related to the extension of a tax rate incentive in China		$ 500