Benefit Plans - Financial Information on Changes in Benefit Obligation, Plan Assets Funded and Balance Sheets Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2022	Aug. 31, 2021	Aug. 31, 2020
Change in plan assets: [Abstract]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 39,000
Pension Benefits
Change in plan assets: [Abstract]
Fair value of plan assets at beginning of period	993,124
Fair value of plan assets at end of period	787,422	$ 993,124
Other Benefits
Change in benefit obligation:
Projected benefit obligation at beginning of period	29,069	30,316
Service cost	996	1,186	$ 1,050
Assumption change	(4,979)	(398)
Plan Amendments	0	0
Settlements	0	0
Benefits paid	(1,801)	(1,763)
Projected benefit obligation at end of period	24,524	29,069	30,316
Change in plan assets: [Abstract]
Fair value of plan assets at beginning of period	0	0
Actual gain (loss) on plan assets	0	0
Defined Benefit Plan, Plan Assets, Contributions by Employer	1,801	1,763
Benefits Paid	(1,801)	(1,763)
Fair value of plan assets at end of period	0	0	0
Funded Status of Plan	(24,524)	(29,069)
ASSETS
Non-current assets	0	0
Liabilities [Abstract]
Current liabilities	(2,290)	(1,970)
Non-current liabilities	(22,234)	(27,099)
Ending balance	(24,524)	(29,069)
Amounts recognized in accumulated other comprehensive loss (pretax): [Abstract]
Prior service cost (credit)	(1,825)	(2,270)
Net (gain) loss	(17,846)	(14,862)
Ending balance	(19,671)	(17,132)
Qualified Pension Benefits | Pension Benefits
Change in benefit obligation:
Projected benefit obligation at beginning of period	925,239	918,002
Service cost	46,275	45,229	42,151
Assumption change	(164,543)	(12,847)
Plan Amendments	132	113
Settlements	0	0
Benefits paid	(77,913)	(76,779)
Projected benefit obligation at end of period	759,173	925,239	918,002
Change in plan assets: [Abstract]
Fair value of plan assets at beginning of period	993,124	976,542
Actual gain (loss) on plan assets	(166,789)	70,161
Defined Benefit Plan, Plan Assets, Contributions by Employer	39,000	23,200
Benefits Paid	(77,913)	(76,779)
Fair value of plan assets at end of period	787,422	993,124	976,542
Funded Status of Plan	28,249	67,885
ASSETS
Non-current assets	28,249	67,885
Liabilities [Abstract]
Current liabilities	0	0
Non-current liabilities	0	0
Ending balance	28,249	67,885
Amounts recognized in accumulated other comprehensive loss (pretax): [Abstract]
Prior service cost (credit)	831	873
Net (gain) loss	235,399	199,785
Ending balance	236,230	200,658
Nonqualified Pension Benefits | Pension Benefits
Change in benefit obligation:
Projected benefit obligation at beginning of period	20,604	19,183
Service cost	926	433	405
Assumption change	(2,892)	(55)
Plan Amendments	0	0
Settlements	(1,327)	0
Benefits paid	(691)	(1,264)
Projected benefit obligation at end of period	18,257	20,604	19,183
Change in plan assets: [Abstract]
Fair value of plan assets at beginning of period	0	0
Actual gain (loss) on plan assets	0	0
Defined Benefit Plan, Plan Assets, Contributions by Employer	2,018	1,264
Benefits Paid	(2,018)	(1,264)
Fair value of plan assets at end of period	0	0	$ 0
Funded Status of Plan	(18,257)	(20,604)
ASSETS
Non-current assets	0	0
Liabilities [Abstract]
Current liabilities	(2,300)	(2,220)
Non-current liabilities	(15,957)	(18,384)
Ending balance	(18,257)	(20,604)
Amounts recognized in accumulated other comprehensive loss (pretax): [Abstract]
Prior service cost (credit)	(274)	(388)
Net (gain) loss	3,257	5,579
Ending balance	$ 2,983	$ 5,191