Retirement Benefit Plans - Changes in the Fair Value of Level 3 Defined Benefit Plan Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Changes in the fair value of the Company's Level 3 investments
Plan assets at beginning of year	$ 22,052	$ 21,691
Actual return on plan assets	622	2,118
Plan assets at end of year	20,970	22,052
Level 3
Changes in the fair value of the Company's Level 3 investments
Plan assets at beginning of year	1,815	2,175
Actual return on plan assets	190	1
Purchases and sales of plan assets, net	0	(361)
Plan assets at end of year	$ 2,005	$ 1,815