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, 2023	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 17,194	$ 17,937	$ 23,211
Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	17,194
Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		16,108
Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	1,829	$ 2,108
Large value
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	879	393
Large value | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	879
Large value | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		393
Large value | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Large blend
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	3,124	7,637
Large blend | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	3,124
Large blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		7,637
Large blend | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Large growth
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,060	302
Large growth | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,060
Large growth | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		302
Large growth | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Mid blend
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	599	167
Mid blend | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	599
Mid blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		167
Mid blend | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Small blend
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	499	359
Small blend | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	499
Small blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		359
Small blend | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Foreign large blend
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	615	1,276
Foreign large blend | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	615
Foreign large blend | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		1,276
Foreign large blend | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Diversified emerging markets
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	272	63
Diversified emerging markets | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	272
Diversified emerging markets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		63
Diversified emerging markets | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Global equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	577
Global equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	577
Inflation protected bond
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	971
Inflation protected bond | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value
Inflation protected bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		971
Inflation protected bond | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Intermediate term bond
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	5,676	6,332
Intermediate term bond | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	5,676
Intermediate term bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		4,503
Intermediate term bond | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		1,829
Multi-sector bond
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	2,044
Multi-sector bond | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	2,044
High inflation bond
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		78
High inflation bond | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		78
High inflation bond | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Emerging markets bonds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Emerging markets bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Emerging markets bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
Cash or money market
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1,849
Cash or money market | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 1,849
Short-term bonds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		359
Short-term bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		359
Short-term bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		$ 0