New Accounting Standards (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Right-of-use asset		$ 22,709
Lease liability		24,114
Cumulative effect adjustment		(1,162,933)	$ (1,900,249)	$ (1,840,551)	$ (1,755,000)
Retained Earnings
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cumulative effect adjustment		$ 57,169	(657,475)	$ (553,014)	$ (445,747)
Cumulative Effect, Period of Adoption, Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cumulative effect adjustment	[1]		182
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cumulative effect adjustment	[1]		182
Accounting Standards Update 2016-02
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Right-of-use asset			19,900
Lease liability			20,900
Accounting Standards Update 2016-02 | Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cumulative effect adjustment			$ 200

[1] Cumulative effect adjustment relates to the adoption of ASU 2016-02, Leases (Topic 872).and related ASUs on October 1, 2019. See Note 2, "New Accounting Pronouncements," for additional information.