Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2016	May 31, 2015
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 9,383	$ 8,889	$ 28,149	$ 27,005
Interest costs	7,691	7,003	23,075	21,019
Expected return on assets	(12,013)	(12,431)	(36,040)	(37,305)
Prior service cost (credit) amortization	402	407	1,205	1,223
Actuarial loss (gain) amortization	4,765	4,916	14,294	14,724
Periodic benefit costs, net	10,228	8,784	30,683	26,666
Defined Benefit Plan, Contributions by Employer			43,400
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	258	206	776	656
Interest costs	352	357	1,055	1,061
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	57	57	171	171
Actuarial loss (gain) amortization	172	272	518	794
Periodic benefit costs, net	839	892	2,520	2,682
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	353	188	1,059	1,134
Interest costs	427	288	1,282	1,118
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(30)	(30)	(90)	(90)
Actuarial loss (gain) amortization	(116)	(342)	(348)	(553)
Periodic benefit costs, net	$ 634	$ 104	$ 1,903	$ 1,609