Retirement Benefit Plans - Changes in the Fair Value of Level 3 Defined Benefit Plan Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Changes in the fair value of the Company's Level 3 investments
Plan assets at beginning of year	$ 17,937	$ 23,211
Actual return on plan assets	979	(3,376)
Plan assets at end of year	17,194	17,937
Level 3
Changes in the fair value of the Company's Level 3 investments
Plan assets at beginning of year	1,829	2,108
Actual return on plan assets	94	(279)
Purchases and sales of plan assets, net	(1,923)	0
Plan assets at end of year	$ 0	$ 1,829