Summary Of Significant Accounting Policies (Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at Beginning of Period	$ (56,150)	$ (28,690)	$ (52,155)	$ (67,750)
Other Comprehensive Gains and Losses Before Reclassifications	55,450	(18,601)	55,825	13,797
Amounts Reclassified From Other Comprehensive Income (Loss)	(18,217)	3,411	(23,537)	17,510
Cumulative Effect of Adoption of Authoritative Guidance for Hedging			950
Reclassification Adjustment for the Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities				(7,437)
Reclassification of Stranded Tax Effects Related to the 2017 Tax Reform Act	0	(10,406)	0	(10,406)
Balance at End of Period	(18,917)	(54,286)	(18,917)	(54,286)
Gains And Losses On Derivative Financial Instruments [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at Beginning of Period	30,680		34,675
Other Comprehensive Gains and Losses Before Reclassifications	55,450		55,825
Amounts Reclassified From Other Comprehensive Income (Loss)	(18,217)		(23,537)
Cumulative Effect of Adoption of Authoritative Guidance for Hedging			950
Balance at End of Period	67,913		67,913
Gains And Losses On Derivative Financial Instruments [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at Beginning of Period		17,886		(28,611)
Other Comprehensive Gains and Losses Before Reclassifications		(18,601)		13,797
Amounts Reclassified From Other Comprehensive Income (Loss)		3,411		17,510
Reclassification Adjustment for the Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities				0
Reclassification of Stranded Tax Effects Related to the 2017 Tax Reform Act		1,866		1,866
Balance at End of Period		4,562		4,562
Gains And Losses On Securities Available For Sale [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at Beginning of Period	0	0	0	7,437
Other Comprehensive Gains and Losses Before Reclassifications	0	0	0	0
Amounts Reclassified From Other Comprehensive Income (Loss)	0	0	0	0
Cumulative Effect of Adoption of Authoritative Guidance for Hedging			0
Reclassification Adjustment for the Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities				(7,437)
Reclassification of Stranded Tax Effects Related to the 2017 Tax Reform Act		0		0
Balance at End of Period	0	0	0	0
Funded Status Of The Pension And Other Post-Retirement Benefit Plans [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at Beginning of Period	(86,830)	(46,576)	(86,830)	(46,576)
Other Comprehensive Gains and Losses Before Reclassifications	0	0	0	0
Amounts Reclassified From Other Comprehensive Income (Loss)	0	0	0	0
Cumulative Effect of Adoption of Authoritative Guidance for Hedging			0
Reclassification Adjustment for the Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities				0
Reclassification of Stranded Tax Effects Related to the 2017 Tax Reform Act		(12,272)		(12,272)
Balance at End of Period	$ (86,830)	$ (58,848)	$ (86,830)	$ (58,848)