Benefit Plans - Rollforward of Benefit Obligation and Plan Assets Funded (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 31,387	$ 26,010	$ 25,232
Interest costs	25,445	24,119	22,257
Expected return on assets	(49,728)	(40,904)	(41,770)
Settlement of retiree obligations
Prior service cost (credit) amortization	1,597	1,831	2,327
Actuarial loss (gain) amortization	22,615	15,131	16,090
Transition amount amortization
Periodic benefit costs, net	31,316	26,187	24,136
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	3.80%	5.00%	4.75%
Expected return on plan assets	7.25%	7.25%	7.75%
Rate of compensation increase	4.50%	4.50%	4.50%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	4.80%	3.80%	5.00%
Rate of compensation increase	4.85%	4.50%	4.50%
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	721	279	1,246
Interest costs	1,316	1,343	1,933
Expected return on assets
Settlement of retiree obligations			4,735
Prior service cost (credit) amortization	228	228	141
Actuarial loss (gain) amortization	921	428	967
Transition amount amortization
Periodic benefit costs, net	3,186	2,278	9,022
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.25%	5.00%	4.75%
Rate of compensation increase	4.75%	4.75%	4.75%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	4.50%	4.00%	5.00%
Rate of compensation increase	4.75%	4.75%	4.50%
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	2,936	2,556	1,771
Interest costs	2,275	2,638	2,194
Expected return on assets
Settlement of retiree obligations
Prior service cost (credit) amortization	(120)	(104)	(122)
Actuarial loss (gain) amortization	1,104	891	513
Transition amount amortization	562	936	935
Periodic benefit costs, net	$ 6,757	$ 6,917	$ 5,291
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	3.75%	4.75%	4.75%
Rate of compensation increase	4.50%	4.50%	4.50%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	3.75%	3.75%	4.75%
Rate of compensation increase	4.50%	4.50%	4.50%