Interim Pension and Other Postretirement Benefit Plan Information (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	May 31, 2021	May 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Settlements		$ (9,000)
Contribution to postretirement medical plans				$ 16,800
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate (in percent)						3.11%	2.80%
Service cost		4,609	$ 4,652	13,834	$ 13,957
Interest cost		5,016	5,843	15,072	17,529
Expected return on assets		(6,978)	(7,079)	(20,934)	(21,237)
Amortization of prior service cost (credit)		(58)	(58)	(174)	(174)
Amortization of actuarial (gain) loss		3,062	3,242	9,405	9,725
Settlements		8,999	0	8,999	0
Net periodic pension cost		14,650	6,600	26,202	19,800
Pension Benefits | Forecast
Defined Benefit Plan Disclosure [Line Items]
Decrease in net periodic pension cost	$ 500
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		4,305	3,366	12,917	10,099
Interest cost		2,661	2,653	7,981	7,959
Expected return on assets		(2,613)	(2,625)	(7,841)	(7,874)
Amortization of prior service cost (credit)		44	43	130	130
Amortization of actuarial (gain) loss		0	(334)	0	(1,003)
Settlements		0	0	0	0
Net periodic pension cost		4,397	$ 3,103	13,187	$ 9,311
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