Benefit Plans - Rollforward of Benefit Obligation and Plan Assets Funded (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 26,010	$ 25,232	$ 20,774
Interest costs	24,119	22,257	23,034
Expected return on assets	(40,904)	(41,770)	(36,875)
Settlement of retiree obligations
Special agreements
Prior service cost (credit) amortization	1,831	2,327	2,193
Actuarial loss (gain) amortization	15,131	16,090	10,578
Transition amount amortization
Periodic benefit costs, net	26,187	24,136	19,704
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	5.00%	4.75%	5.75%
Expected return on plan assets	7.25%	7.75%	8.25%
Rate of compensation increase	4.50%	4.50%	4.50%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	3.80%	5.00%	4.75%
Rate of compensation increase	4.50%	4.50%	4.50%
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	279	1,246	1,220
Interest costs	1,343	1,933	2,235
Expected return on assets
Settlement of retiree obligations		4,735
Special agreements
Prior service cost (credit) amortization	228	141	419
Actuarial loss (gain) amortization	428	967	617
Transition amount amortization
Periodic benefit costs, net	2,278	9,022	4,491
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	5.00%	4.75%	5.75%
Rate of compensation increase	4.75%	4.75%	4.50%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	4.00%	5.00%	4.75%
Rate of compensation increase	4.75%	4.50%	4.50%
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	2,556	1,771	1,385
Interest costs	2,638	2,194	2,153
Expected return on assets
Settlement of retiree obligations
Special agreements			1,722
Prior service cost (credit) amortization	(104)	(122)	(186)
Actuarial loss (gain) amortization	891	513	12
Transition amount amortization	936	935	936
Periodic benefit costs, net	$ 6,917	$ 5,291	$ 6,022
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.75%	4.75%	5.75%
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%	4.75%	4.75%
Rate of compensation increase	4.50%	4.50%	4.50%