Benefit Plans - Net Periodic Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2013	May 31, 2012
Pension Plans, Defined Benefit [Member]
Component of net periodic benefit costs: [Abstract]
Service costs	$ 9,109	$ 6,505	$ 23,541	$ 19,508
Interest costs	6,072	5,942	19,078	17,786
Expected return on assets	(13,388)	(10,004)	(37,311)	(30,013)
Prior service cost (credit) amortization	399	458	1,198	1,374
Actuarial loss (gain) amortization	6,500	3,809	16,961	11,285
Transition amount amortization
Periodic benefit costs, net	8,692	6,710	23,467	19,940
Defined Benefit Plan, Contributions by Employer			23,800
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	211	68	540	209
Interest costs	340	346	987	1,041
Expected return on assets
Prior service cost (credit) amortization	57	57	171	171
Actuarial loss (gain) amortization	270	109	692	334
Transition amount amortization
Periodic benefit costs, net	878	580	2,390	1,755
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	935	896	2,202	1,917
Interest costs	443	672	1,675	1,945
Expected return on assets
Prior service cost (credit) amortization	(81)	(26)	(90)	(78)
Actuarial loss (gain) amortization	371	243	817	656
Transition amount amortization	73	234	422	702
Periodic benefit costs, net	$ 1,741	$ 2,019	$ 5,026	$ 5,142