Description of Business and Summary of Significant Accounting Policies (Change in AOCI, Net of Tax) (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 1,900,758	$ 1,963,380	$ 2,368,344
Other comprehensive (loss) income before reclassifications	2,004
Amounts reclassified from AOCI	46,622
Total other comprehensive income (loss)	48,626	(63,395)	(74,019)
Ending Balance	1,825,399	1,900,758	1,963,380
Foreign Currency Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(14,298)
Other comprehensive (loss) income before reclassifications	(22,297)
Amounts reclassified from AOCI	0
Total other comprehensive income (loss)	(22,297)
Ending Balance	(36,595)	(14,298)
Derivative Instruments
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(39,398)
Other comprehensive (loss) income before reclassifications	(6,004)
Amounts reclassified from AOCI	14,406
Total other comprehensive income (loss)	8,402
Ending Balance	(30,996)	(39,398)
Actuarial (Loss) Gain
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(28,033)
Other comprehensive (loss) income before reclassifications	66,285
Amounts reclassified from AOCI	(4,159)
Total other comprehensive income (loss)	62,126
Ending Balance	34,093	(28,033)
Actuarial (loss) gain is net of tax	(12,000)
Prior Service Cost
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(608)
Other comprehensive (loss) income before reclassifications	(17)
Amounts reclassified from AOCI	(45)
Total other comprehensive income (loss)	(62)
Ending Balance	(670)	(608)
Available for Sale Securities
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(457)
Other comprehensive (loss) income before reclassifications	(35,963)
Amounts reclassified from AOCI	36,420
Total other comprehensive income (loss)	457
Ending Balance	0	(457)
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(82,794)	(19,399)	54,620
Total other comprehensive income (loss)	48,626	(63,395)	(74,019)
Ending Balance	$ (34,168)	$ (82,794)	$ (19,399)