Retirement Benefit Plans - Changes in the Fair Value of Level 3 Defined Benefit Plan Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Changes in the fair value of the Company's Level 3 investments
Plan assets at beginning of year	$ 21,691	$ 21,344
Actual return on plan assets	2,118	1,978
Plan assets at end of year	22,052	21,691
Level 3
Changes in the fair value of the Company's Level 3 investments
Plan assets at beginning of year	2,175	2,185
Actual return on plan assets	1	26
Purchases and sales of plan assets, net	(361)	(36)
Plan assets at end of year	$ 1,815	$ 2,175