Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Basic Earnings Per Share
Net income	$ 1,042,895	$ 885,862	$ 774,398
Less: Income allocated to participating securities	553	542	508
Net income available to common shareholders	$ 1,042,342	$ 885,320	$ 773,890
Basic weighted average shares outstanding (in shares)	152,508	145,121	137,830
Net income per share — Basic (USD per share)	$ 6.83	$ 6.10	$ 5.61
Diluted Earnings Per Share
Net income available to common shareholders	$ 1,042,342	$ 885,320	$ 773,890
Effect of dilutive shares	0	0	0
Net income available to common shareholders	$ 1,042,342	$ 885,320	$ 773,890
Basic weighted average shares outstanding (in shares)	152,508	145,121	137,830
Dilutive shares (in shares)	158	45	266
Diluted weighted average shares outstanding (in shares)	152,666	145,166	138,096
Net income per share — Diluted (USD per share)	$ 6.83	$ 6.10	$ 5.60