Pension Plan and Retirement Benefits - Plan Assets (Details) $ in Thousands	Sep. 30, 2022 USD ($) item	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Defined Benefit Pension Plan
Asset allocation
Total pension plan assets	$ 218,321	$ 297,703	$ 245,546
Defined Benefit Pension Plan | Fair Value, Inputs, Level 1 [Member]
Asset allocation
Total pension plan assets	15,926	23,654
Defined Benefit Pension Plan | Fair Value, Inputs, Level 2 [Member]
Asset allocation
Total pension plan assets	158,582	169,953
Defined Benefit Pension Plan | NAV
Asset allocation
Total pension plan assets	$ 43,813	104,096
Pension Plans Defined Benefit Us [Member]
Defined Benefit Plans
Number of issuances of fixed income securities | item	305
Number of issuers of fixed income securities | item	251
Asset allocation
Total pension plan assets	$ 203,216	274,267
Pension Plans Defined Benefit Us [Member] | U.S. corporate and government bonds
Asset allocation
Total pension plan assets	174,508	193,607
Pension Plans Defined Benefit Us [Member] | Mutual Fund [Member]
Asset allocation
Total pension plan assets	16,471	44,743
Pension Plans Defined Benefit Us [Member] | U.S. common stock
Asset allocation
Total pension plan assets	6,847	19,672
Pension Plans Defined Benefit Us [Member] | International equity
Asset allocation
Total pension plan assets	5,390	16,245
Pension Plans Defined Benefit Us [Member] | Fair Value, Inputs, Level 1 [Member]
Asset allocation
Total pension plan assets	15,926	23,654
Pension Plans Defined Benefit Us [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. corporate and government bonds
Asset allocation
Total pension plan assets	15,926	23,654
Pension Plans Defined Benefit Us [Member] | Fair Value, Inputs, Level 2 [Member]
Asset allocation
Total pension plan assets	158,582	169,953
Pension Plans Defined Benefit Us [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. corporate and government bonds
Asset allocation
Total pension plan assets	158,582	169,953
Pension Plans Defined Benefit Us [Member] | NAV
Asset allocation
Total pension plan assets	28,708	80,660
Pension Plans Defined Benefit Us [Member] | NAV | Mutual Fund [Member]
Asset allocation
Total pension plan assets	16,471	44,743
Pension Plans Defined Benefit Us [Member] | NAV | U.S. common stock
Asset allocation
Total pension plan assets	6,847	19,672
Pension Plans Defined Benefit Us [Member] | NAV | International equity
Asset allocation
Total pension plan assets	5,390	16,245
Pension Plans Defined Benefit Non Us [Member]
Asset allocation
Total pension plan assets	15,105	23,436
Pension Plans Defined Benefit Non Us [Member] | Bonds [Member]
Asset allocation
Total pension plan assets	8,006	12,890
Pension Plans Defined Benefit Non Us [Member] | Equity
Asset allocation
Total pension plan assets	5,135	8,202
Pension Plans Defined Benefit Non Us [Member] | Other
Asset allocation
Total pension plan assets	1,964	2,344
Pension Plans Defined Benefit Non Us [Member] | NAV
Asset allocation
Total pension plan assets	15,105	23,436
Pension Plans Defined Benefit Non Us [Member] | NAV | Bonds [Member]
Asset allocation
Total pension plan assets	8,006	12,890
Pension Plans Defined Benefit Non Us [Member] | NAV | Equity
Asset allocation
Total pension plan assets	5,135	8,202
Pension Plans Defined Benefit Non Us [Member] | NAV | Other
Asset allocation
Total pension plan assets	$ 1,964	$ 2,344