CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Sep. 30, 2019
Statement of Financial Position [Abstract]
Allowance for loan losses	$ 139,501	$ 131,534
Goodwill	$ 302,691	$ 301,368
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	135,742,217	135,539,806
Common stock, shares outstanding (in shares)	75,706,100	78,841,463
Treasury stock, shares (in shares)	60,036,117	56,698,343