Income Taxes - Unrecognized Tax Benefits - General Information (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Uncertainties [Abstract]
Unrecognized tax benefits	$ 17,310	$ 3,243	$ 3,378	$ 5,427
Unrecognized tax benefits, tax benefits that if recognized would impact the effective tax rate	17,310
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense [Abstract]
Interest related to unrecognized benefits	1,100	$ 100	$ 100
Anticipated unrecognized tax benefit reduction during next twelve months	$ 100

Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

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Amount of unrecognized tax benefits.

+ References

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Amount of interest expense for an underpayment of income taxes.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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