Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Aug. 31, 2018	Aug. 31, 2017
Deferred tax assets:
Accrued expenses	$ 138,417	$ 227,877
Postretirement health care and deferred compensation	41,797	82,682
Tax credit carryforwards	154,240	169,549
Loss carryforwards	104,519	156,615
Nonqualified equity	178,046	140,009
Major maintenance	5,484	13,011
Other	83,580	83,138
Deferred tax assets valuation reserve	(230,373)	(289,082)
Total deferred tax assets	475,710	583,799
Deferred tax liabilities:
Pension	19,397	32,150
Investments	98,608	130,816
Property, plant and equipment	513,238	709,313
Other	26,828	40,323
Total deferred tax liabilities	658,071	912,602
Net deferred tax liabilities	$ 182,361	$ 328,803