Stock-Based Compensation Plans - Schedule of Nonvested Stock Award Activity (Details) - Nonvested Stock Units - $ / shares	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares
Unvested shares, beginning balance (in shares)	1,817,300
Granted (in shares)	525,500
Performance adjustments (in shares)	(2,200)
Vested (in shares)	(609,400)
Forfeited (in shares)	(252,800)
Modified (in shares)	(127,800)
Unvested shares, ending balance (in shares)	1,350,600	1,817,300
Unvested shares beginning balance, weighted average grant date fair value (usd per share)	$ 25.53
Granted, weighted average grant date fair value (in usd per share)	33.98	$ 35.32	$ 22.33
Performance adjustments, weighted average grant date fair value (in usd per share)	30.58
Vested, weighted average grant date fair value (in usd per share)	25.68
Forfeitures, weighted average grant date fair value (in usd per share)	33.94
Modified, weighted average grant date fair value (in usd per share)	35.48
Unvested shares ending balance, weighted average grant date fair value (usd per share)	$ 33.35	$ 25.53