Income Taxes - Provision (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income tax expense (benefit)	$ 6,288	$ 3,400	$ 11,058	$ 437
Benefit related to stock compensation windfalls			$ 2,700	6,100
Benefit from a reduction of deferred tax liabilities related to the extension of a tax rate incentive in China				$ 500