Derivative Financial Instruments and Hedging Activities - Fair Value of Derivative Instruments Designated as Fair Value Hedges (Details) - USD ($) $ in Thousands	Aug. 31, 2018	Aug. 31, 2017
Derivative [Line Items]
Derivative asset	$ 352,029	$ 249,661
Derivative liability	445,755	313,261
Designated as Hedging Instrument | Interest rate swap derivatives
Derivative [Line Items]
Derivative asset	0	9,978
Derivative liability	9,452	707
Designated as Hedging Instrument | Derivative assets | Interest rate swap derivatives
Derivative [Line Items]
Derivative asset	0	0
Designated as Hedging Instrument | Derivative liabilities | Interest rate swap derivatives
Derivative [Line Items]
Derivative liability	771	0
Designated as Hedging Instrument | Other assets | Interest rate swap derivatives
Derivative [Line Items]
Derivative asset	0	9,978
Designated as Hedging Instrument | Other liabilities | Interest rate swap derivatives
Derivative [Line Items]
Derivative liability	$ 8,681	$ 707