Retirement and Postretirement Employee Benefit Plans - Schedule of Employee Pension Plans Investments at Fair Value (Details) - Employee Pension Plan - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Derivatives, Fair Value [Line Items]
Total investments	$ 624,503	$ 595,212	$ 502,412
Fair Value, Recurring
Derivatives, Fair Value [Line Items]
Total investments	619,429	594,491
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3
Derivatives, Fair Value [Line Items]
Total investments	499,028	459,723
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Common stocks
Derivatives, Fair Value [Line Items]
Total investments	284,573	289,301
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Money market funds
Derivatives, Fair Value [Line Items]
Total investments	16,293	14,542
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Registered investment companies
Derivatives, Fair Value [Line Items]
Total investments	123,022	90,086
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Mortgage-backed securities
Derivatives, Fair Value [Line Items]
Total investments	26,101	24,383
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | U.S. treasuries
Derivatives, Fair Value [Line Items]
Total investments	15,047	9,425
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds
Derivatives, Fair Value [Line Items]
Total investments	32,517	31,986
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Asset-backed securities
Derivatives, Fair Value [Line Items]
Total investments	1,475
Fair Value, Recurring | Level 1
Derivatives, Fair Value [Line Items]
Total investments	422,616	388,785
Fair Value, Recurring | Level 1 | Common stocks
Derivatives, Fair Value [Line Items]
Total investments	284,573	289,301
Fair Value, Recurring | Level 1 | Money market funds
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Registered investment companies
Derivatives, Fair Value [Line Items]
Total investments	123,022	90,086
Fair Value, Recurring | Level 1 | Mortgage-backed securities
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | U.S. treasuries
Derivatives, Fair Value [Line Items]
Total investments	15,021	9,398
Fair Value, Recurring | Level 1 | Corporate bonds
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Asset-backed securities
Derivatives, Fair Value [Line Items]
Total investments	0
Fair Value, Recurring | Level 2
Derivatives, Fair Value [Line Items]
Total investments	76,412	70,938
Fair Value, Recurring | Level 2 | Common stocks
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 2 | Money market funds
Derivatives, Fair Value [Line Items]
Total investments	16,293	14,542
Fair Value, Recurring | Level 2 | Registered investment companies
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 2 | Mortgage-backed securities
Derivatives, Fair Value [Line Items]
Total investments	26,101	24,383
Fair Value, Recurring | Level 2 | U.S. treasuries
Derivatives, Fair Value [Line Items]
Total investments	26	27
Fair Value, Recurring | Level 2 | Corporate bonds
Derivatives, Fair Value [Line Items]
Total investments	32,517	31,986
Fair Value, Recurring | Level 2 | Asset-backed securities
Derivatives, Fair Value [Line Items]
Total investments	1,475
Fair Value, Recurring | Level 3
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Common stocks
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Money market funds
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Registered investment companies
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Mortgage-backed securities
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | U.S. treasuries
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Corporate bonds
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Asset-backed securities
Derivatives, Fair Value [Line Items]
Total investments	0
Fair Value, Recurring | Fair Value Measured at Net Asset Value Per Share | Common/collective trusts
Derivatives, Fair Value [Line Items]
Total investments	95,558	111,103
Fair Value, Recurring | Fair Value Measured at Net Asset Value Per Share | Limited partnerships
Derivatives, Fair Value [Line Items]
Total investments	$ 24,843	$ 23,665