CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Common stock shares outstanding, balance (in shares) at Sep. 30, 2021		132,419,754
Shareholders' equity, beginning balance at Sep. 30, 2021	$ 7,906,889	$ 662	$ 5,023,751	$ 69,803	$ 2,812,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	774,398				774,398
Other comprehensive income (loss)	299,309			299,309
Cash dividends	(375,914)				(375,914)
Common stock issued:
Public offering (in shares)		7,907,883
Public offering	776,805	$ 40	776,765
Direct stock purchase plan (in shares)		68,693
Direct stock purchase plan	7,495		7,495
Retirement savings plan (in shares)		72,339
Retirement savings plan	7,908		7,908
1998 Long-term incentive plan (in shares)		427,929
1998 Long-term incentive plan	2,398	$ 2	2,396
Employee stock-based compensation	19,803		19,803
Common stock shares outstanding, ending balance (in shares) at Sep. 30, 2022		140,896,598
Shareholders' equity, ending balance at Sep. 30, 2022	9,419,091	$ 704	5,838,118	369,112	3,211,157
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	885,862				885,862
Other comprehensive income (loss)	149,416			149,416
Cash dividends	(430,345)				(430,345)
Common stock issued:
Public offering (in shares)		7,272,261
Public offering	806,949	$ 36	806,913
Direct stock purchase plan (in shares)		64,871
Direct stock purchase plan	7,429		7,429
Retirement savings plan (in shares)		69,716
Retirement savings plan	7,966	$ 1	7,965
1998 Long-term incentive plan (in shares)		189,337
1998 Long-term incentive plan	2,108	$ 1	2,107
Employee stock-based compensation	$ 21,588		21,588
Common stock shares outstanding, ending balance (in shares) at Sep. 30, 2023	148,492,783	148,492,783
Shareholders' equity, ending balance at Sep. 30, 2023	$ 10,870,064	$ 742	6,684,120	518,528	3,666,674
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,042,895				1,042,895
Other comprehensive income (loss)	(52,813)			(52,813)
Cash dividends	(492,950)				(492,950)
Common stock issued:
Public offering (in shares)		6,401,469
Public offering	749,987	$ 32	749,955
Direct stock purchase plan (in shares)		60,756
Direct stock purchase plan	7,129		7,129
Retirement savings plan (in shares)		67,134
Retirement savings plan	7,955	$ 1	7,954
1998 Long-term incentive plan (in shares)		236,703
1998 Long-term incentive plan	2,198	$ 1	2,197
Employee stock-based compensation	$ 23,204		23,204
Common stock shares outstanding, ending balance (in shares) at Sep. 30, 2024	155,258,845	155,258,845
Shareholders' equity, ending balance at Sep. 30, 2024	$ 12,157,669	$ 776	$ 7,474,559	$ 465,715	$ 4,216,619