Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($)	3 Months Ended		6 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	$ 9,920,000	$ 11,692,000	$ 19,839,000	$ 21,075,000
Interest cost	5,991,000	3,812,000	11,992,000	11,504,000
Expected return on assets	(12,049,000)	(12,101,000)	(24,089,000)	(24,115,000)
Prior service cost (credit) amortization	360,000	368,000	719,000	770,000
Actuarial (gain) loss amortization	4,511,000	6,650,000	11,399,000	11,415,000
Net periodic benefit cost	8,733,000	10,421,000	19,860,000	20,649,000
Defined Benefit Plan, Plan Assets, Contributions by Employer			0
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	137,000	344,000	274,000	603,000
Interest cost	178,000	70,000	356,000	422,000
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	7,000	(47,000)	15,000	10,000
Actuarial (gain) loss amortization	16,000	100,000	30,000	273,000
Net periodic benefit cost	338,000	467,000	675,000	1,308,000
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	236,000	227,000	472,000	580,000
Interest cost	227,000	39,000	454,000	466,000
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(142,000)	(253,000)	(283,000)	(283,000)
Actuarial (gain) loss amortization	(306,000)	(283,000)	(612,000)	(399,000)
Net periodic benefit cost	$ 15,000	$ (270,000)	$ 31,000	$ 364,000