Consolidated Statements Of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net Income (Loss) Available for Common Stock	$ 112,436	$ (106,068)	$ 190,210	$ (19,477)
Other Comprehensive Income (Loss), Before Tax:
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(34,373)	76,304	13,648	76,799
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income	3,666	(25,034)	3,977	(32,386)
Cumulative Effect of Adoption of Authoritative Guidance for Hedging	0	0	0	1,313
Other Comprehensive Income (Loss), Before Tax	(30,707)	51,270	17,625	45,726
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(9,470)	20,854	3,760	20,974
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income	1,010	(6,817)	1,096	(8,849)
Income Tax Benefit (Expense) on Cumulative Effect of Adoption of Authoritative Guidance for Hedging	0	0	0	363
Income Taxes – Net	(8,460)	14,037	4,856	12,488
Other Comprehensive Income (Loss)	(22,247)	37,233	12,769	33,238
Comprehensive Income (Loss)	$ 90,189	$ (68,835)	$ 202,979	$ 13,761