Shareholders' Equity - Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted average shares outstanding (in shares)	65,192,510	65,287,650	72,529,188
Weighted average diluted shares (in shares)	65,255,283	65,404,110	72,565,920
Net income available to common shareholders, basic	$ 242,801	$ 221,705	$ 173,581
Net income available to common shareholders, diluted	$ 242,801	$ 221,705	$ 173,581
Basic EPS (in dollars per share)	$ 3.72	$ 3.40	$ 2.39
Diluted EPS (in dollars per share)	$ 3.72	$ 3.39	$ 2.39
Options
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted average dilutive options (in shares)	62,773	116,460	36,732