Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2024	Mar. 31, 2023
Basic Earnings Per Share
Net income	$ 432,023	$ 311,292	$ 357,671	$ 271,860	$ 743,315	$ 629,531
Less: Income allocated to participating securities	255		212		442	381
Income available to common shareholders	$ 431,768		$ 357,459		$ 742,873	$ 629,150
Basic weighted average shares outstanding (in shares)	151,271		143,941		150,534	142,881
Net income per share - Basic (USD per share)	$ 2.85		$ 2.48		$ 4.93	$ 4.40
Diluted Earnings Per Share
Income available to common shareholders	$ 431,768		$ 357,459		$ 742,873	$ 629,150
Effect of dilutive shares	0		0		0	0
Income available to common shareholders	$ 431,768		$ 357,459		$ 742,873	$ 629,150
Basic weighted average shares outstanding (in shares)	151,271		143,941		150,534	142,881
Dilutive shares (in shares)	26		46		13	82
Diluted weighted average shares outstanding (in shares)	151,297		143,987		150,547	142,963
Net income per share - Diluted (USD per share)	$ 2.85		$ 2.48		$ 4.93	$ 4.40