Retirement and Postretirement Employee Benefit Plans - Schedule of Net Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Employee Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other non-operating income (expense)	Other non-operating income (expense)	Other non-operating income (expense)
Components of net periodic postretirement cost:
Service cost	$ 16,165	$ 17,369	$ 17,551
Interest cost	17,606	16,883	19,028
Expected return on assets	(29,531)	(27,913)	(28,316)
Amortization of prior service credit	(231)	(231)	(231)
Recognized actuarial loss	4,638	8,686	9,025
Net periodic pension cost	$ 8,647	$ 14,794	$ 17,057
Supplemental Executive Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other non-operating income (expense)	Other non-operating income (expense)	Other non-operating income (expense)
Components of net periodic postretirement cost:
Service cost	$ 1,129	$ 1,067	$ 1,074
Interest cost	2,647	3,180	4,188
Recognized actuarial loss	3,166	3,560	3,945
Settlements	0	9,151	9,180
Net periodic pension cost	$ 6,942	$ 16,958	$ 18,387
Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other non-operating income (expense)	Other non-operating income (expense)	Other non-operating income (expense)
Components of net periodic postretirement cost:
Service cost	$ 10,235	$ 11,000	$ 13,466
Interest cost	10,734	15,372	10,612
Expected return on assets	(13,249)	(10,455)	(10,499)
Amortization of prior service credit	(13,234)	30,533	173
Recognized actuarial loss	0	1,172	(1,337)
Net periodic pension cost	$ (5,514)	$ 47,622	$ 12,415