Retirement Benefit Plans - Asset Allocation of Defined Benefit Pension Plan Assets and Fair Values and Levels in Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 23,211	$ 21,609	$ 20,970
Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	21,103	19,511
Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	2,108	2,098	$ 2,005
Large value
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	514	175
Large value | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	514	175
Large value | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Large blend
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	10,227	9,334
Large blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	10,227	9,334
Large blend | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Large growth
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	519	1,109
Large growth | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	519	1,109
Large growth | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Mid blend
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	223	176
Mid blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	223	176
Mid blend | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Small blend
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	697	224
Small blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	697	224
Small blend | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Foreign large blend
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,807	1,603
Foreign large blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,807	1,603
Foreign large blend | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Diversified emerging markets
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	86	50
Diversified emerging markets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	86	50
Diversified emerging markets | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Inflation protected bond
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,087	1,028
Inflation protected bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,087	1,028
Inflation protected bond | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Intermediate term bond
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	7,396	7,479
Intermediate term bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	5,288	5,381
Intermediate term bond | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	2,108	2,098
High inflation bond
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	189	178
High inflation bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	189	178
High inflation bond | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Emerging markets bonds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	164	106
Emerging markets bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	164	106
Emerging markets bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Short-term bonds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	302	147
Short-term bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	302	147
Short-term bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 0	$ 0