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, 2021			95,710,000
Balance as of beginning of period at Sep. 30, 2021		$ 1,630,862	$ 240,644	$ 502,584	$ (34,528)	$ (12,448)	$ 934,610
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		111,312					111,312
Other comprehensive income		1,030			1,030
Common stock issued:
Incentive compensation plan (in shares)			147,000
Incentive compensation plan		7,502	$ 367	7,135
Dividend reinvestment plan (in shares)			105,000
Dividend reinvestment plan		3,678	$ 263	3,415
Cash dividend declared		(34,787)					(34,787)
Treasury stock and other		(2,619)				(2,619)
Balance as of end of period (in shares) at Dec. 31, 2021			95,962,000
Balance as of end of period at Dec. 31, 2021		$ 1,716,978	$ 241,274	513,134	(33,498)	(15,067)	1,011,135
Balance as of beginning of period (in shares) at Sep. 30, 2022		96,249,859	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		115,921					115,921
Other comprehensive income		304			304
Common stock issued:
Incentive compensation plan (in shares)			92,000
Incentive compensation plan		3,472	$ 229	3,243
Dividend reinvestment plan (in shares)	[1]		93,000
Dividend reinvestment plan	[1]	3,866		437		3,429
Waiver discount (in shares)			368,000
Waiver discount		17,919		4,469		13,450
Cash dividend declared		(37,665)					(37,665)
Treasury stock and other		$ 1,768				1,768
Balance as of end of period (in shares) at Dec. 31, 2022		96,803,490	96,803,000
Balance as of end of period at Dec. 31, 2022		$ 1,922,795	$ 241,845	$ 527,846	$ (4,522)	$ 11,842	$ 1,145,784

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