Benefit Plans - Changes in Benefit Obligation and Plan (Details) (USD $)	12 Months Ended
	Aug. 31, 2014	Aug. 31, 2013	Aug. 31, 2012
Qualified Pension Benefits
Change in benefit obligation: [Rollforward]
Benefit obligation at beginning of period	$ 641,284,000	$ 671,066,000
Service cost	30,417,000	31,387,000	26,010,000
Interest cost	29,900,000	25,445,000	24,119,000
Actuarial loss (gain)	1,973,000	12,819,000
Assumption change	57,406,000	(64,483,000)
Plan Amendments	647,000	0
Medicare D	0	0
Benefits Paid	(40,734,000)	(34,950,000)
Benefit obligation at end of period	720,893,000	641,284,000	671,066,000
Change in plan assets: [Abstract]
Fair value of plan assets at beginning of period	730,628,000	688,196,000
Actual gain on plan assets	106,531,000	53,582,000
Company contributions	25,700,000	23,800,000
Benefits Paid	(40,734,000)	(34,950,000)
Fair value of plan assets at end of period	822,125,000	730,628,000	688,196,000
Funded Status of Plan	101,232,000	89,344,000
Assets [Abstract]
Non-current assets	103,125,000	89,930,000
Liabilities [Abstract]
Current liabilities	0	0
Non-current liabilities	(1,893,000)	(586,000)
Ending balance	101,232,000	89,344,000
Amounts recognized in accumulated other comprehensive loss (pretax): [Abstract]
Prior service cost (credit)	6,848,000	7,794,000
Net loss	235,564,000	253,288,000
Ending balance	242,412,000	261,082,000
Non-Qualified Pension Benefits
Change in benefit obligation: [Rollforward]
Benefit obligation at beginning of period	36,225,000	34,470,000
Service cost	860,000	721,000	279,000
Interest cost	1,660,000	1,316,000	1,343,000
Actuarial loss (gain)	393,000	3,455,000
Assumption change	2,421,000	(1,952,000)
Plan Amendments	0	0
Medicare D	0	0
Benefits Paid	(3,576,000)	(1,785,000)
Benefit obligation at end of period	37,983,000	36,225,000	34,470,000
Change in plan assets: [Abstract]
Fair value of plan assets at beginning of period	0	0
Actual gain on plan assets	0	0
Company contributions	3,576,000	1,785,000
Benefits Paid	(3,576,000)	(1,785,000)
Fair value of plan assets at end of period	0	0	0
Funded Status of Plan	(37,983,000)	(36,225,000)
Assets [Abstract]
Non-current assets	0	0
Liabilities [Abstract]
Current liabilities	(3,222,000)	(3,051,000)
Non-current liabilities	(34,761,000)	(33,174,000)
Ending balance	(37,983,000)	(36,225,000)
Amounts recognized in accumulated other comprehensive loss (pretax): [Abstract]
Prior service cost (credit)	859,000	1,088,000
Net loss	12,542,000	10,685,000
Ending balance	13,401,000	11,773,000
Other Benefits
Change in benefit obligation: [Rollforward]
Benefit obligation at beginning of period	45,542,000	64,189,000
Service cost	1,729,000	2,936,000	2,556,000
Interest cost	1,918,000	2,275,000	2,638,000
Actuarial loss (gain)	(4,135,000)	(5,243,000)
Assumption change	1,425,000	(16,693,000)
Plan Amendments	0	0
Medicare D	0	92,000
Benefits Paid	(2,161,000)	(2,014,000)
Benefit obligation at end of period	44,318,000	45,542,000	64,189,000
Change in plan assets: [Abstract]
Fair value of plan assets at beginning of period	0	0
Actual gain on plan assets	0	0
Company contributions	2,161,000	2,014,000
Benefits Paid	(2,161,000)	(2,014,000)
Fair value of plan assets at end of period	0	0	0
Funded Status of Plan	(44,318,000)	(45,542,000)
Assets [Abstract]
Non-current assets	0	0
Liabilities [Abstract]
Current liabilities	(2,787,000)	(2,919,000)
Non-current liabilities	(41,531,000)	(42,623,000)
Ending balance	(44,318,000)	(45,542,000)
Amounts recognized in accumulated other comprehensive loss (pretax): [Abstract]
Prior service cost (credit)	(592,000)	(712,000)
Net loss	(7,573,000)	(5,415,000)
Ending balance	$ (8,165,000)	$ (6,127,000)