Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Basic Earnings Per Share
Net income	$ 885,862	$ 774,398	$ 665,563
Less: Income allocated to participating securities	542	508	465
Net income available to common shareholders	$ 885,320	$ 773,890	$ 665,098
Basic weighted average shares outstanding (in shares)	145,121	137,830	129,779
Net income per share — Basic (USD per share)	$ 6.10	$ 5.61	$ 5.12
Diluted Earnings Per Share
Net income available to common shareholders	$ 885,320	$ 773,890	$ 665,098
Effect of dilutive shares	0	0	0
Net income available to common shareholders	$ 885,320	$ 773,890	$ 665,098
Basic weighted average shares outstanding (in shares)	145,121	137,830	129,779
Dilutive shares (in shares)	45	266	55
Diluted weighted average shares outstanding (in shares)	145,166	138,096	129,834
Net income per share — Diluted (USD per share)	$ 6.10	$ 5.60	$ 5.12