Benefit Plans - Net Periodic Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Nov. 30, 2013	Nov. 30, 2012
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 7,467	$ 7,216
Interest costs	6,698	6,505
Expected return on assets	(12,734)	(11,956)
Prior service cost (credit) amortization	399	399
Actuarial loss (gain) amortization	4,644	5,231
Transition amount amortization
Periodic benefit costs, net	6,474	7,395
Defined Benefit Plan, Contributions by Employer	0
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	179	165
Interest costs	336	323
Expected return on assets
Prior service cost (credit) amortization	57	57
Actuarial loss (gain) amortization	227	211
Transition amount amortization
Periodic benefit costs, net	799	756
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	482	633
Interest costs	519	616
Expected return on assets
Prior service cost (credit) amortization	(30)	(4)
Actuarial loss (gain) amortization		223
Transition amount amortization	124	175
Periodic benefit costs, net	$ 1,095	$ 1,643