Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($)	3 Months Ended		9 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2019	May 31, 2018
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	$ 9,648,000	$ 9,920,000	$ 28,944,000	$ 29,758,000
Interest cost	7,099,000	5,997,000	21,297,000	17,988,000
Expected return on assets	(11,242,000)	(12,044,000)	(33,726,000)	(36,133,000)
Prior service cost (credit) amortization	42,000	360,000	127,000	1,078,000
Actuarial (gain) loss amortization	3,087,000	4,905,000	9,261,000	16,304,000
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment			169,000
Net periodic benefit cost	8,634,000	9,138,000	26,072,000	28,995,000
Defined Benefit Plan, Plan Assets, Contributions by Employer			40,000,000
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	78,000	137,000	233,000	411,000
Interest cost	186,000	177,000	560,000	533,000
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(19,000)	7,000	(56,000)	23,000
Actuarial (gain) loss amortization	1,000	16,000	2,000	46,000
Net periodic benefit cost	246,000	337,000	739,000	1,013,000
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	263,000	236,000	790,000	707,000
Interest cost	274,000	227,000	821,000	681,000
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(139,000)	(142,000)	(417,000)	(424,000)
Actuarial (gain) loss amortization	(407,000)	(306,000)	(1,221,000)	(918,000)
Net periodic benefit cost	$ (9,000)	$ 15,000	$ (27,000)	$ 46,000