Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2022	Aug. 31, 2021	Aug. 31, 2020
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 996	$ 1,186	$ 1,050
Expected return on assets	0	0	0
Settlement of retiree obligations	0	0	0
Amortization of actuarial (gain) loss	(1,259)	(1,365)	(1,392)
Periodic benefit costs, net	$ (205)	$ (131)	$ (40)
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	2.57%	2.43%	2.89%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	4.64%	2.57%	2.43%
Amortization of prior service (credit) costs	$ (445)	$ (445)	$ (445)
Other Benefits | interest cost
Component of net periodic benefit costs: [Abstract]
Periodic benefit costs, net	503	493	747
Other Benefits | experience study
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Actuarial (gain) loss	19	(317)
Other Benefits | Other demographic experience
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Actuarial (gain) loss	717	(448)
Qualified Pension Benefits | Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	46,275	45,229	42,151
Settlement of retiree obligations	0	0	0
Amortization of actuarial (gain) loss	23,406	21,790	21,583
Periodic benefit costs, net	$ 43,064	$ 40,119	$ 38,950
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	2.80%	2.65%	3.06%
Expected return on plan assets	4.88%	4.90%	5.50%
Rate of compensation increase	4.79%	4.99%	5.28%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	4.69%	2.78%	2.67%
Rate of compensation increase	4.93%	4.79%	4.99%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate	4.65%	4.65%	4.65%
Amortization of prior service (credit) costs	$ 174	$ 178	$ 178
Qualified Pension Benefits | Pension Benefits | interest cost
Component of net periodic benefit costs: [Abstract]
Periodic benefit costs, net	17,167	16,563	21,722
Qualified Pension Benefits | Pension Benefits | expected return on asset
Component of net periodic benefit costs: [Abstract]
Periodic benefit costs, net	(43,958)	(43,641)	(46,684)
Qualified Pension Benefits | Pension Benefits | experience study
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Actuarial (gain) loss	2,941	23,716
Qualified Pension Benefits | Pension Benefits | Other demographic experience
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Actuarial (gain) loss	9,875	11,242
Nonqualified Pension Benefits | Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	926	433	405
Expected return on assets	0	0	0
Settlement of retiree obligations	0	0	0
Amortization of actuarial (gain) loss	478	212	98
Periodic benefit costs, net	$ 1,571	$ 804	$ 818
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	2.04%	2.07%	2.70%
Rate of compensation increase	4.79%	4.99%	5.28%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	4.49%	2.08%	2.15%
Rate of compensation increase	4.93%	4.79%	4.99%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate	4.65%	4.65%	4.65%
Amortization of prior service (credit) costs	$ (114)	$ (114)	$ (114)
Nonqualified Pension Benefits | Pension Benefits | interest cost
Component of net periodic benefit costs: [Abstract]
Periodic benefit costs, net	281	273	$ 429
Nonqualified Pension Benefits | Pension Benefits | experience study
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Actuarial (gain) loss	43	1,272
Nonqualified Pension Benefits | Pension Benefits | Other demographic experience
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Actuarial (gain) loss	$ 1,313	$ 762