Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Operating Loss Carryforwards [Line Items]
Income tax expense (benefit)	$ (12,456)	$ (104,076)	$ (181,124)
Deferred Tax Liabilities, Net	142,900	182,361
Income (Loss) from Continuing Operations before Income Taxes, Domestic	825,700	717,400	158,500
Income (Loss) from Continuing Operations before Income Taxes, Foreign	$ (3,100)	$ (46,200)	$ (268,700)
Statutory federal income tax rate	21.00%	25.70%	35.00%
Operating Loss Carryforwards	$ 626,400
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	363,600
Change in valuation allowance for deferred tax asset	15,100
Amount of unrecognized tax benefits that would benefit effective tax rate	93,300
Unrecognized Tax Benefits, Interest on Income Taxes Expense	1,700	$ 1,200
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	2,900	1,200
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	0	0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	0
Other assets
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	100	400
State tax credit
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	123,000
Alternative minimum tax credit
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	14,100
Low sulfer diesel credits
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	79,300
NCRA
Operating Loss Carryforwards [Line Items]
Change in valuation allowance for deferred tax asset	800
NCRA | State tax credit
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	123,300	$ 121,600
Foreign tax authority | Fiscal year 2018
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	$ 11,200