CONDENSED CONSOLIDATED STATEMENTS OF COMMON STOCK EQUITY (Unaudited) - 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, 2023		97,584,000
Balance as of beginning 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	89,411					89,411
Other comprehensive income	395			395
Common stock issued:
Incentive compensation plan (in shares)		116,000
Incentive compensation plan	3,741	$ 290	3,451
Dividend reinvestment plan (in shares)		94,000
Dividend reinvestment plan	3,788	$ 236	3,552
Waiver discount (in shares)		410,000
Waiver discount	17,919	$ 1,025	16,894
Cash dividend declared	(41,176)					(41,176)
Treasury stock and other (in shares)		(2,000)
Treasury stock and other	1,388				1,388
Balance as of end of period (in shares) at Dec. 31, 2023		98,202,000
Balance as of end of period at Dec. 31, 2023	2,066,201	$ 245,009	582,551	(9,564)	22,136	1,226,069
Balance as of beginning of period (in shares) at Sep. 30, 2023		97,584,000
Balance as of beginning 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	210,223
Other comprehensive income	10,281
Balance as of end of period (in shares) at Mar. 31, 2024		98,745,000
Balance as of end of period at Mar. 31, 2024	2,179,225	$ 246,367	604,009	322	22,936	1,305,591
Balance as of beginning of period (in shares) at Dec. 31, 2023		98,202,000
Balance as of beginning of period at Dec. 31, 2023	2,066,201	$ 245,009	582,551	(9,564)	22,136	1,226,069
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	120,812					120,812
Other comprehensive income	9,886			9,886
Common stock issued:
Incentive compensation plan (in shares)		25,000
Incentive compensation plan	1,242	$ 64	1,178
Dividend reinvestment plan (in shares)		84,000
Dividend reinvestment plan	3,655	$ 209	3,446
Waiver discount (in shares)		435,000
Waiver discount	17,919	$ 1,085	16,834
Cash dividend declared	(41,290)					(41,290)
Treasury stock and other (in shares)		(1,000)
Treasury stock and other	800				800
Balance as of end of period (in shares) at Mar. 31, 2024		98,745,000
Balance as of end of period at Mar. 31, 2024	$ 2,179,225	$ 246,367	604,009	322	22,936	1,305,591
Balance as of beginning of period (in shares) at Sep. 30, 2024	99,461,448	99,461,000
Balance as of beginning 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	131,319					131,319
Other comprehensive income	68			68
Common stock issued:
Incentive compensation plan (in shares)		232,000
Incentive compensation plan	8,242	$ 581	7,661
Dividend reinvestment plan (in shares)		80,000
Dividend reinvestment plan	3,744	$ 199	3,545
Waiver discount (in shares)		418,000
Waiver discount	19,910	$ 1,045	18,865
Cash dividend declared	(45,010)					(45,010)
Treasury stock and other	(6,032)				(6,032)
Balance as of end of period (in shares) at Dec. 31, 2024		100,191,000
Balance as of end of period at Dec. 31, 2024	$ 2,312,684	$ 249,984	663,882	(6,453)	20,188	1,385,083
Balance as of beginning of period (in shares) at Sep. 30, 2024	99,461,448	99,461,000
Balance as of beginning 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	335,606
Other comprehensive income	$ 135
Balance as of end of period (in shares) at Mar. 31, 2025	100,302,638	100,303,000
Balance as of end of period at Mar. 31, 2025	$ 2,477,907	$ 250,265	668,599	(6,386)	21,194	1,544,235
Balance as of beginning of period (in shares) at Dec. 31, 2024		100,191,000
Balance as of beginning of period at Dec. 31, 2024	2,312,684	$ 249,984	663,882	(6,453)	20,188	1,385,083
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	204,287					204,287
Other comprehensive income	67			67
Common stock issued:
Incentive compensation plan (in shares)		31,000
Incentive compensation plan	1,275	$ 76	1,199
Dividend reinvestment plan (in shares)		81,000
Dividend reinvestment plan	3,723	$ 205	3,518
Cash dividend declared	(45,135)					(45,135)
Treasury stock and other	$ 1,006				1,006
Balance as of end of period (in shares) at Mar. 31, 2025	100,302,638	100,303,000
Balance as of end of period at Mar. 31, 2025	$ 2,477,907	$ 250,265	$ 668,599	$ (6,386)	$ 21,194	$ 1,544,235