Retirement and Post-Retirement Employee Benefit Plans - Schedule of Employee Pension Plans Investments at Fair Value (Details) - Defined Benefit Plan - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Derivatives, Fair Value [Line Items]
Total investments	$ 596,806	$ 528,881	$ 530,109
Fair Value, Recurring
Derivatives, Fair Value [Line Items]
Total investments	594,730	528,154
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3
Derivatives, Fair Value [Line Items]
Total investments	372,861	336,771
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Common stocks
Derivatives, Fair Value [Line Items]
Total investments	239,166	211,244
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Money market funds
Derivatives, Fair Value [Line Items]
Total investments	7,060	6,096
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Registered investment companies
Derivatives, Fair Value [Line Items]
Total investments	74,236	29,762
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Mortgage-backed securities
Derivatives, Fair Value [Line Items]
Total investments	14,048	15,230
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | U.S. treasuries
Derivatives, Fair Value [Line Items]
Total investments	7,517	21,791
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds
Derivatives, Fair Value [Line Items]
Total investments	30,834	52,648
Fair Value, Recurring | Level 1
Derivatives, Fair Value [Line Items]
Total investments	320,885	262,761
Fair Value, Recurring | Level 1 | Common stocks
Derivatives, Fair Value [Line Items]
Total investments	239,166	211,244
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	74,236	29,762
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	7,483	21,755
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	51,976	74,010
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	7,060	6,096
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	14,048	15,230
Fair Value, Recurring | Level 2 | U.S. treasuries
Derivatives, Fair Value [Line Items]
Total investments	34	36
Fair Value, Recurring | Level 2 | Corporate bonds
Derivatives, Fair Value [Line Items]
Total investments	30,834	52,648
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	121,570	122,207
Fair Value, Recurring | Fair Value Measured at Net Asset Value Per Share | Limited partnerships
Derivatives, Fair Value [Line Items]
Total investments	$ 100,299	$ 69,176