CONSOLIDATED STATEMENTS OF COMMON STOCK EQUITY - USD ($) $ in Thousands		Total	Common Stock	Premium on Common Stock	Accumulated Other Comprehensive (Loss) Income	Treasury Stock And Other	Retained Earnings
Balance as of beginning of period (in shares) at Sep. 30, 2022			96,250,000
Balance as of beginning of period at Sep. 30, 2022		$ 1,817,210	$ 241,616	$ 519,697	$ (4,826)	$ (6,805)	$ 1,067,528
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		264,724					264,724
Other comprehensive income (loss)		(5,133)			(5,133)
Common stock issued:
Incentive compensation plan (in shares)			136,000
Incentive compensation plan		5,168	$ 339	4,829
Dividend reinvestment plan (in shares)	[1]		258,000
Dividend reinvestment plan	[1]	15,034	$ 205	6,069		8,760
Waiver discount (in shares)			948,000
Waiver discount		42,807	$ 1,298	28,059		13,450
Cash dividend declared		(154,418)					(154,418)
Treasury stock and other (in shares)			(8,000)
Treasury stock and other		5,343				5,343
Balance as of end of period (in shares) at Sep. 30, 2023			97,584,000
Balance as of end of period at Sep. 30, 2023		1,990,735	$ 243,458	558,654	(9,959)	20,748	1,177,834
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		289,775					289,775
Other comprehensive income (loss)		3,438			3,438
Common stock issued:
Incentive compensation plan (in shares)			154,000
Incentive compensation plan		5,484	$ 385	5,099
Dividend reinvestment plan (in shares)	[1]		346,000
Dividend reinvestment plan	[1]	14,644	$ 864	13,780
Waiver discount (in shares)			1,380,000
Waiver discount		59,730	$ 3,452	56,278
Cash dividend declared		(168,835)					(168,835)
Treasury stock and other (in shares)			(3,000)
Treasury stock and other		$ 5,472				5,472
Balance as of end of period (in shares) at Sep. 30, 2024		99,461,448	99,461,000
Balance as of end of period at Sep. 30, 2024		$ 2,200,443	$ 248,159	633,811	(6,521)	26,220	1,298,774
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		335,627					335,627
Other comprehensive income (loss)		(4,942)			(4,942)
Common stock issued:
Incentive compensation plan (in shares)			283,000
Incentive compensation plan		10,613	$ 708	9,905
Dividend reinvestment plan (in shares)	[1]		318,000
Dividend reinvestment plan	[1]	14,847	$ 793	14,054
Waiver discount (in shares)			418,000
Waiver discount		19,910	$ 1,045	18,865
Cash dividend declared		(183,034)					(183,034)
Treasury stock and other (in shares)			(1,000)
Treasury stock and other		$ (1,798)				(1,798)
Balance as of end of period (in shares) at Sep. 30, 2025		100,478,590	100,479,000
Balance as of end of period at Sep. 30, 2025		$ 2,391,666	$ 250,705	$ 676,635	$ (11,463)	$ 24,422	$ 1,451,367

[1] Certain shares sold through the DRP issued from treasury stock are at average cost, which may differ from the actual market price paid.