Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Aug. 31, 2017	Aug. 31, 2016
Deferred Tax Assets, Gross [Abstract]
Accrued expenses	$ 226,964	$ 87,251
Postretirment health care and deferred compensation	82,682	111,983
Deferred Tax Assets, Tax Credit Carryforwards	166,213	143,252
Deferred Tax Assets, Operating Loss Carryforwards	169,724	155,966
Deferred Tax Assets, Nonqualified Equity	152,835	30,168
Other	55,119	30,627
Deferred tax assets valuation	(284,716)	(194,277)
Deferred tax assets	568,821	364,970
Deferred Tax Liabilities, Gross [Abstract]
Pension	31,050	26,516
Investments	129,985	107,716
Major maintenance	2,115	4,970
Property, plant and equipment	712,195	681,160
Deferred Tax Liabilities, Other	25,964	29,905
Deferred Tax Liabilities, Gross	901,309	850,267
Net deferred tax liabilities	$ 332,488	$ 485,297