Benefit Plans - Net Periodic Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Nov. 30, 2012	Nov. 30, 2011
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 7,216	$ 6,502
Interest costs	6,505	5,935
Expected return on assets	(11,956)	(10,024)
Prior service cost (credit) amortization	399	458
Actuarial loss (gain) amortization	5,231	3,732
Transition amount amortization
Periodic benefit costs, net	7,395	6,603
Defined Benefit Plan, Contributions by Employer	0
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	165	172
Interest costs	323	348
Expected return on assets
Prior service cost (credit) amortization	57	57
Actuarial loss (gain) amortization	211	112
Transition amount amortization
Periodic benefit costs, net	756	689
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	633	510
Interest costs	616	636
Expected return on assets
Prior service cost (credit) amortization	(4)	(26)
Actuarial loss (gain) amortization	223	207
Transition amount amortization	175	234
Periodic benefit costs, net	$ 1,643	$ 1,561