Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2015	May. 31, 2014
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 8,889	$ 7,543	$ 27,005	$ 22,812
Interest costs	7,003	7,495	21,019	22,433
Expected return on assets	(12,431)	(11,910)	(37,305)	(35,726)
Prior service cost (credit) amortization	407	398	1,223	1,195
Actuarial loss (gain) amortization	4,916	4,566	14,724	13,655
Periodic benefit costs, net	8,784	8,092	26,666	24,369
Defined Benefit Plan, Contributions by Employer			29,100
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	206	219	656	646
Interest costs	357	423	1,061	1,245
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	57	57	171	171
Actuarial loss (gain) amortization	272	250	794	718
Periodic benefit costs, net	892	949	2,682	2,780
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	188	339	1,134	1,297
Interest costs	288	418	1,118	1,439
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(30)	(30)	(90)	(90)
Actuarial loss (gain) amortization	(342)	(228)	(553)	(415)
Periodic benefit costs, net	$ 104	$ 499	$ 1,609	$ 2,231