Income Taxes - Tax valuation allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Tax valuation allowance
Deferred tax asset valuation allowance	$ 59,817	$ 69,098
Decrease in valuation allowance	9,300
Net tax benefit before offset by amounts recorded through OCI	9,000
Deferred tax liability	74,379	$ 41,397
Foreign
Tax valuation allowance
Deferred tax liability	$ 2,200