Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2025	Mar. 31, 2024
Basic Earnings Per Share
Net income	$ 485,576	$ 351,858	$ 432,023	$ 311,292	$ 837,434	$ 743,315
Less: Income allocated to participating securities	245		255		436	442
Income available to common shareholders	$ 485,331		$ 431,768		$ 836,998	$ 742,873
Basic weighted average shares outstanding (in shares)	159,177		151,271		157,739	150,534
Net income per share - Basic (USD per share)	$ 3.05		$ 2.85		$ 5.31	$ 4.93
Diluted Earnings Per Share
Income available to common shareholders	$ 485,331		$ 431,768		$ 836,998	$ 742,873
Effect of dilutive shares	0		0		0	0
Income available to common shareholders	$ 485,331		$ 431,768		$ 836,998	$ 742,873
Basic weighted average shares outstanding (in shares)	159,177		151,271		157,739	150,534
Dilutive shares (in shares)	1,249		26		1,386	13
Diluted weighted average shares outstanding (in shares)	160,426		151,297		159,125	150,547
Net income per share - Diluted (USD per share)	$ 3.03		$ 2.85		$ 5.26	$ 4.93