Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2020	May 31, 2019
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	$ 10,538	$ 9,648	$ 31,613	$ 28,944
Interest cost	5,431	7,099	16,292	21,297
Expected return on assets	(11,671)	(11,242)	(35,013)	(33,726)
Prior service cost (credit) amortization	45	42	134	127
Actuarial (gain) loss amortization	5,396	3,087	16,187	9,261
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment			0	169
Net periodic benefit cost	9,739	8,634	29,213	26,072
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	101	78	304	233
Interest cost	107	186	322	560
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(28)	(19)	(85)	(56)
Actuarial (gain) loss amortization	25	1	74	2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment			0	0
Net periodic benefit cost	205	246	615	739
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	262	263	787	790
Interest cost	187	274	560	821
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(111)	(139)	(334)	(417)
Actuarial (gain) loss amortization	(348)	(407)	(1,044)	(1,221)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment			0	0
Net periodic benefit cost	$ (10)	$ (9)	$ (31)	$ (27)