Derivative Financial Instruments and Hedging Activities Derivatives (Details) - USD ($)	3 Months Ended					6 Months Ended
	Feb. 28, 2017	Nov. 30, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Feb. 28, 2017	Feb. 29, 2016	Aug. 31, 2016
Purchase and Sales Contracts [Line Items]
Credit Rating Agencies Threshold, Minimum						66.67%
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 376,993,000					$ 376,993,000		$ 510,945,000
Derivative Asset, Fair Value, Gross Asset, Current	386,613,000					386,613,000
Derivative Asset, Not offset, Policy election deduction, Current	30,160,000					30,160,000
Derivative Asset, Fair Value, Amount not offset against collateral, Current	356,453,000					356,453,000
Derivative Asset, Fair Value, Gross Asset	407,153,000					407,153,000		543,821,000
Derivative Asset, Fair Value, Gross Amount Not Offset on Balance Sheet	30,160,000					30,160,000		32,876,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	245,244,000					245,244,000		479,912,000
Derivative Liability, Fair Value, Gross Liability	275,484,000					275,484,000		513,599,000
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	80,000					80,000		811,000
Derivative Liability, Fair Value, Gross Amount Not Offset on Balance Sheet	30,160,000					30,160,000		32,876,000
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net						0
CF Nitrogen LLC [Member]
Purchase and Sales Contracts [Line Items]
Annual Payment Receivable Contingent On Investment Credit Rating						5,000,000
Payments For Credit Rating Decrease In Investment		$ 5,000,000
Embedded derivative asset	24,600,000	24,100,000				24,600,000
Embedded Derivative, Gain on Embedded Derivative	500,000	$ 29,100,000
Foreign currency derivatives | Not Designated as Hedging Instrument [Member]
Purchase and Sales Contracts [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	17,231,000					17,231,000		12,364,000
Derivative Asset, Fair Value, Gross Asset	27,548,000					27,548,000		21,551,000
Derivative Asset, Fair Value, Gross Amount Not Offset on Balance Sheet	10,317,000					10,317,000		9,187,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	8,220,000					8,220,000		13,102,000
Derivative Liability, Fair Value, Gross Liability	18,537,000					18,537,000		22,289,000
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0					0		0
Derivative Liability, Fair Value, Gross Amount Not Offset on Balance Sheet	10,317,000					10,317,000		9,187,000
Derivative Asset, Notional Amount	903,400,000					903,400,000		802,200,000
Interest rate swap derivatives | Designated as Hedging Instrument [Member]
Purchase and Sales Contracts [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	6,892,000					6,892,000		22,078,000
Derivative Asset, Fair Value, Gross Asset	6,892,000					6,892,000		22,078,000
Derivative Asset, Fair Value, Gross Amount Not Offset on Balance Sheet	0					0		0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	2,327,000					2,327,000
Derivative Liability, Fair Value, Gross Liability	2,327,000					2,327,000
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0					0
Derivative Liability, Fair Value, Gross Amount Not Offset on Balance Sheet	0					0
Interest rate swap derivatives | Not Designated as Hedging Instrument [Member]
Purchase and Sales Contracts [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	2,000					2,000		8,000
Derivative Liability, Fair Value, Gross Liability	2,000					2,000		8,000
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0					0		0
Derivative Liability, Fair Value, Gross Amount Not Offset on Balance Sheet	0					0		0
Commodity and freight derivatives | Not Designated as Hedging Instrument [Member]
Purchase and Sales Contracts [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	328,301,000					328,301,000		476,503,000
Derivative Asset, Fair Value, Gross Asset	348,144,000					348,144,000		500,192,000
Derivative Asset, Fair Value, Gross Amount Not Offset on Balance Sheet	19,843,000					19,843,000		23,689,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	234,695,000					234,695,000		466,802,000
Derivative Liability, Fair Value, Gross Liability	254,618,000					254,618,000		491,302,000
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	80,000					80,000		811,000
Derivative Liability, Fair Value, Gross Amount Not Offset on Balance Sheet	19,843,000					19,843,000		23,689,000
Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Purchase and Sales Contracts [Line Items]
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge						17,500,000	$ 11,500,000
Fair Value Hedging [Member] | Interest rate swap derivatives | Designated as Hedging Instrument [Member]
Purchase and Sales Contracts [Line Items]
Derivative Asset, Notional Amount	495,000,000					495,000,000
Cash Flow Hedging [Member] | Interest rate swap derivatives | Designated as Hedging Instrument [Member]
Purchase and Sales Contracts [Line Items]
Derivative Asset, Notional Amount								$ 300,000,000
Cash paid to settle derivative			$ 5,100,000	$ 5,300,000	$ 6,400,000
Derivatives settled, number			2	2	2
Derivatives [Member] | Embedded Derivative Financial Instruments [Member] | Not Designated as Hedging Instrument [Member]
Purchase and Sales Contracts [Line Items]
Derivative Asset, Fair Value, Gross Asset, Current	4,029,000					4,029,000
Derivative Asset, Not offset, Policy election deduction, Current	0					0
Derivative Asset, Fair Value, Amount not offset against collateral, Current	4,029,000					4,029,000
Other Assets [Member] | Embedded Derivative Financial Instruments [Member] | Not Designated as Hedging Instrument [Member]
Purchase and Sales Contracts [Line Items]
Derivative Asset, Fair Value, Gross Asset, Non-current	20,540,000					20,540,000
Derivative Asset, Not offset, Policy election deduction, Non-current	0					0
Derivative Asset, Fair Value, Amount not offset against collateral, Non-current	$ 20,540,000					$ 20,540,000