Accounting Changes and Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net decrease in noncurrent deferred income tax liabilities	$ (69,700)	$ (98,036)
ASU 2015-17
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Decrease in current deferred income tax assets		(28,400)
Net decrease in noncurrent deferred income tax liabilities		(22,100)
ASU 2015-17 | Other Assets
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net increase in noncurrent deferred income tax assets		4,300
ASU 2015-17 | Accrued Liabilities
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Decrease in current deferred income tax liabilities		$ (2,000)
ASU 16-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Estimated amount of Right of use asset	600,000
Lease liability	$ 600,000