Accumulated Other Comprehensive Income - Change in AOCI, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 1,905,513	$ 2,344,692	$ 1,963,380	$ 2,368,344
Other comprehensive (loss) income before reclassifications			(11,540)
Amounts reclassified from AOCI			17,686
Total other comprehensive income	18,695	35,124	6,146	31,988
Ending Balance	1,858,852	2,294,346	1,858,852	2,294,346
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			7,431
Other comprehensive (loss) income before reclassifications			12,912
Amounts reclassified from AOCI			0
Total other comprehensive income			12,912
Ending Balance	20,343		20,343
Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			8,116
Other comprehensive (loss) income before reclassifications			(16,083)
Amounts reclassified from AOCI			17,686
Total other comprehensive income			1,603
Ending Balance	9,719		9,719
Actuarial (Loss) Gain
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(25,021)
Other comprehensive (loss) income before reclassifications			103
Amounts reclassified from AOCI			0
Total other comprehensive income			103
Ending Balance	(24,918)		(24,918)
Prior Service Cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(643)
Other comprehensive (loss) income before reclassifications			0
Amounts reclassified from AOCI			0
Total other comprehensive income			0
Ending Balance	(643)		(643)
Available for Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(9,282)
Other comprehensive (loss) income before reclassifications			(8,472)
Amounts reclassified from AOCI			0
Total other comprehensive income			(8,472)
Ending Balance	(17,754)		(17,754)
AOCI Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(31,948)	51,484	(19,399)	54,620
Ending Balance	$ (13,253)	$ 86,608	$ (13,253)	$ 86,608