Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2021	Feb. 29, 2020	Feb. 28, 2021	Feb. 29, 2020
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	$ 11,307	$ 10,538	$ 22,614	$ 21,076
Interest cost	4,141	5,431	8,281	10,861
Expected return on assets	(10,910)	(11,671)	(21,821)	(23,342)
Prior service cost (credit) amortization	45	45	89	89
Actuarial loss (gain) amortization	5,447	5,396	10,895	10,791
Net periodic benefit cost (benefit)	10,030	9,739	20,058	19,475
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	108	101	217	203
Interest cost	68	107	136	214
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(28)	(28)	(57)	(57)
Actuarial loss (gain) amortization	53	25	106	49
Net periodic benefit cost (benefit)	201	205	402	409
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service cost	297	262	593	525
Interest cost	123	187	246	374
Expected return on assets	0	0	0	0
Prior service cost (credit) amortization	(111)	(111)	(223)	(223)
Actuarial loss (gain) amortization	(341)	(348)	(682)	(696)
Net periodic benefit cost (benefit)	$ (32)	$ (10)	$ (66)	$ (20)