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, 2019	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 20,970	$ 22,052	$ 21,691
Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	18,965	20,237
Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	2,005	1,815	$ 2,175
Large value
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	435	446
Large value | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	435	446
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	9,368	9,910
Large blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	9,368	9,910
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	625	825
Large growth | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	625	825
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	163	228
Mid blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	163	228
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	159	229
Small blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	159	229
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	1,607	1,714
Foreign large blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,607	1,714
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	17	18
Diversified emerging markets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	17	18
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	1,100	1,184
Inflation protected bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,100	1,184
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	6,974	6,811
Intermediate term bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	4,969	4,996
Intermediate term bond | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	2,005	1,815
High inflation bond
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	173	182
High inflation bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	173	182
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	106	38
Emerging markets bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	106	38
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	243	467
Short-term bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	243	467
Short-term bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 0	$ 0