Interim Pension and Other Postretirement Benefit Plan Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Contribution to postretirement medical plans			$ 7,800
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4,324	$ 4,613	8,647	$ 9,225
Interest cost	5,064	5,028	10,127	10,056
Expected return on assets	(7,383)	(6,978)	(14,766)	(13,956)
Amortization of prior service cost (credit)	(58)	(58)	(116)	(116)
Amortization of actuarial (gain) loss	1,951	3,171	3,902	6,343
Net periodic pension cost	3,898	5,776	7,794	11,552
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,558	4,306	5,117	8,612
Interest cost	2,684	2,660	5,367	5,320
Expected return on assets	(3,313)	(2,614)	(6,625)	(5,228)
Amortization of prior service cost (credit)	(3,308)	43	(6,617)	86
Amortization of actuarial (gain) loss	0	0	0	0
Net periodic pension cost	(1,379)	$ 4,395	(2,758)	$ 8,790
Minimum | Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected future contributions	15,000		15,000
Maximum | Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected future contributions	$ 25,000		$ 25,000