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, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 22,052	$ 21,691	$ 21,344
Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	20,237	19,516
Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,815	2,175	$ 2,185
Large value
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	446	681
Large value | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	446	681
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	9,910	9,788
Large blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	9,910	9,788
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	825	470
Large growth | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	825	470
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	228	79
Mid blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	228	79
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	229	111
Small blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	229	111
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	1,714	1,731
Foreign large blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,714	1,731
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	18	19
Diversified emerging markets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	18	19
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	1,184	1,089
Inflation protected bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,184	1,089
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	6,811	7,240
Intermediate term bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	4,996	5,065
Intermediate term bond | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,815	2,175
High inflation bond
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	182	187
High inflation bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	182	187
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	38	77
Emerging markets bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	38	77
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	467	219
Short-term bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	467	219
Short-term bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 0	$ 0