Consolidated Statements Of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net Income Available for Common Stock	$ 41,250	$ 63,753	$ 21,773	$ 257,009
Other Comprehensive Income (Loss), Before Tax:
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	4,904		81,703
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period		34,211		53,619
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income	(36,347)		(68,733)
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income		(3,869)		20,498
Cumulative Effect of Adoption of Authoritative Guidance for Hedging	0	0	1,313	0
Reclassification Adjustment for the Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities to Earnings Reinvested in the Business	0	0	0	(11,738)
Other Comprehensive Income (Loss), Before Tax	(31,443)	30,342	14,283	62,379
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	1,341		22,315
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period		9,835		15,434
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income	(9,907)		(18,756)
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income		(1,113)		5,756
Income Tax Benefit (Expense) on Cumulative Effect of Adoption of Authoritative Guidance for Hedging	0	0	363	0
Reclassification Adjustment for Income Tax Benefit (Expense) on the Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities to Earnings Reinvested in the Business	0	0	0	(4,301)
Reclassification Adjustment for Stranded Tax Effects Related to the 2017 Tax Reform Act to Earnings Reinvested in the Business	0	0	0	10,406
Income Taxes – Net	(8,566)	8,722	3,922	27,295
Other Comprehensive Income (Loss)	(22,877)	21,620	10,361	35,084
Comprehensive Income	$ 18,373	$ 85,373	$ 32,134	$ 292,093