Retirement and Postretirement Employee Benefit Plans - Schedule of Employee Pension Plans Investments at Fair Value (Details) - Employee Pension Plan - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Derivatives, Fair Value [Line Items]
Total investments	$ 595,212	$ 502,412	$ 479,025
Fair Value, Recurring
Derivatives, Fair Value [Line Items]
Total investments	594,491	501,985
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3
Derivatives, Fair Value [Line Items]
Total investments	459,723	393,534
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Common stocks
Derivatives, Fair Value [Line Items]
Total investments	289,301	243,600
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Money market funds
Derivatives, Fair Value [Line Items]
Total investments	14,542	30,965
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Registered investment companies
Derivatives, Fair Value [Line Items]
Total investments	90,086	69,439
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Mortgage-backed securities
Derivatives, Fair Value [Line Items]
Total investments	24,383	17,685
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | U.S. treasuries
Derivatives, Fair Value [Line Items]
Total investments	9,425	8,488
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds
Derivatives, Fair Value [Line Items]
Total investments	31,986	23,357
Fair Value, Recurring | Level 1
Derivatives, Fair Value [Line Items]
Total investments	388,785	321,500
Fair Value, Recurring | Level 1 | Common stocks
Derivatives, Fair Value [Line Items]
Total investments	289,301	243,600
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	90,086	69,439
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	9,398	8,461
Fair Value, Recurring | Level 1 | Corporate bonds
Derivatives, Fair Value [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 2
Derivatives, Fair Value [Line Items]
Total investments	70,938	72,034
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	14,542	30,965
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	24,383	17,685
Fair Value, Recurring | Level 2 | U.S. treasuries
Derivatives, Fair Value [Line Items]
Total investments	27	27
Fair Value, Recurring | Level 2 | Corporate bonds
Derivatives, Fair Value [Line Items]
Total investments	31,986	23,357
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 | Fair Value Measured at Net Asset Value Per Share | Common/collective trusts
Derivatives, Fair Value [Line Items]
Total investments	111,103	88,122
Fair Value, Recurring | Fair Value Measured at Net Asset Value Per Share | Limited partnerships
Derivatives, Fair Value [Line Items]
Total investments	$ 23,665	$ 20,329