Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($)	3 Months Ended		6 Months Ended
	Feb. 28, 2017	Feb. 29, 2016	Feb. 28, 2017	Feb. 29, 2016
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	$ 11,692,000	$ 9,383,000	$ 21,075,000	$ 18,766,000
Interest cost	3,812,000	7,691,000	11,504,000	15,384,000
Expected return on assets	(12,101,000)	(12,013,000)	(24,115,000)	(24,027,000)
Prior service cost (credit) amortization	368,000	401,000	770,000	803,000
Actuarial (gain) loss amortization	6,650,000	4,775,000	11,415,000	9,529,000
Net periodic benefit cost	10,421,000	10,237,000	20,649,000	20,455,000
Defined Benefit Plan, Contributions by Employer			0
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	344,000	259,000	603,000	518,000
Interest cost	70,000	351,000	422,000	703,000
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(47,000)	57,000	10,000	114,000
Actuarial (gain) loss amortization	100,000	173,000	273,000	346,000
Net periodic benefit cost	467,000	840,000	1,308,000	1,681,000
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	227,000	353,000	580,000	706,000
Interest cost	39,000	428,000	466,000	855,000
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(253,000)	(30,000)	(283,000)	(60,000)
Actuarial (gain) loss amortization	(283,000)	(116,000)	(399,000)	(232,000)
Net periodic benefit cost	$ (270,000)	$ 635,000	$ 364,000	$ 1,269,000