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Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($)
$ in Thousands
 12 Months Ended
Aug. 31, 2025
Aug. 31, 2024
Aug. 31, 2023
experience study      
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]      
Actuarial (gain) loss $ (29) $ 0  
Other demographic experience      
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]      
Actuarial (gain) loss (646) 1,465  
Other Benefits      
Component of net periodic benefit costs: [Abstract]      
Service costs 844 650 $ 670
Expected return on assets 0 0 0
Amortization of actuarial (gain) loss (1,192) (1,616) (1,615)
Periodic benefit costs, net $ 347 $ (267) $ (355)
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]      
Discount rate 5.01% 5.33% 4.64%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]      
Discount rate 5.41% 5.01% 5.33%
Amortization of prior service (credit) costs $ (445) $ (445) $ (445)
Other Benefits | interest cost      
Component of net periodic benefit costs: [Abstract]      
Periodic benefit costs, net 1,140 1,144 1,035
Qualified Pension Benefits | experience study      
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]      
Actuarial (gain) loss 8,394 2,988  
Qualified Pension Benefits | Other demographic experience      
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]      
Actuarial (gain) loss 20,025 18,647  
Qualified Pension Benefits | Pension Benefits      
Component of net periodic benefit costs: [Abstract]      
Service costs 43,727 37,391 38,579
Amortization of actuarial (gain) loss 12,815 1,796 1,872
Periodic benefit costs, net $ 44,662 $ 27,433 $ 28,059
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]      
Discount rate 5.12% 5.38% 4.69%
Expected return on plan assets 5.64% 5.64% 4.88%
Rate of compensation increase 4.98% 4.98% 4.93%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]      
Discount rate 5.61% 5.09% 5.38%
Rate of compensation increase 4.58% 4.98% 4.98%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate 4.31% 4.68% 4.80%
Amortization of prior service (credit) costs $ 199 $ 178 $ 149
Qualified Pension Benefits | Pension Benefits | interest cost      
Component of net periodic benefit costs: [Abstract]      
Periodic benefit costs, net 34,898 35,928 30,588
Qualified Pension Benefits | Pension Benefits | expected return on asset      
Component of net periodic benefit costs: [Abstract]      
Periodic benefit costs, net (46,977) (47,860) (43,129)
Nonqualified Pension Benefits | experience study      
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]      
Actuarial (gain) loss 365 244  
Nonqualified Pension Benefits | Other demographic experience      
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]      
Actuarial (gain) loss 2,862 3,217  
Nonqualified Pension Benefits | Pension Benefits      
Component of net periodic benefit costs: [Abstract]      
Service costs 3,027 1,968 1,840
Expected return on assets 0 0 0
Amortization of actuarial (gain) loss 799 380 245
Periodic benefit costs, net $ 4,933 $ 3,277 $ 2,712
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]      
Discount rate 4.78% 5.22% 4.48%
Rate of compensation increase 4.98% 4.98% 4.93%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]      
Discount rate 4.97% 4.78% 5.23%
Rate of compensation increase 4.58% 4.98% 4.98%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate 4.31% 4.68% 4.80%
Amortization of prior service (credit) costs $ (47) $ (114) $ (114)
Nonqualified Pension Benefits | Pension Benefits | interest cost      
Component of net periodic benefit costs: [Abstract]      
Periodic benefit costs, net $ 1,154 $ 1,043 $ 741