Consolidated Statements Of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income Available for Common Stock	$ 90,595	$ 91,847	$ 193,256	$ 290,501
Other Comprehensive Income (Loss), Before Tax:
Unrealized Gain (Loss) on Securities Available for Sale Arising During the Period	0	(678)	0	(722)
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(26,000)	(12,582)	19,390	(18,081)
Reclassification Adjustment for Realized (Gains) Losses on Securities Available for Sale in Net Income	0	0	0	(430)
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income	4,739	3,199	24,384	(9,349)
Reclassification Adjustment for the Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities to Earnings Reinvested in the Business	0	0	(11,738)	0
Other Comprehensive Income (Loss), Before Tax	(21,261)	(10,061)	32,036	(28,582)
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Securities Available for Sale Arising During the Period	0	(252)	0	(317)
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(7,399)	(3,519)	5,593	(5,824)
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Securities Available for Sale in Net Income	0	0	0	(158)
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income	1,328	551	6,874	(4,646)
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	(4,301)	0
Reclassification Adjustment for Stranded Tax Effects Related to the 2017 Tax Reform Act to Earnings Reinvested in the Business	(10,406)	0	(10,406)	0
Income Taxes – Net	4,335	(3,220)	18,572	(10,945)
Other Comprehensive Income (Loss)	(25,596)	(6,841)	13,464	(17,637)
Comprehensive Income	$ 64,999	$ 85,006	$ 206,720	$ 272,864