Derivative Financial Instruments and Hedging Activities Derivatives (Details) - USD ($)	3 Months Ended						9 Months Ended
	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	May 31, 2017	May 31, 2016	Aug. 31, 2016	Aug. 31, 2015
Purchase and Sales Contracts [Line Items]
Credit Rating Agencies Threshold, Minimum							66.67%
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 377,122,000						$ 377,122,000		$ 510,945,000
Derivative Asset, Fair Value, Gross Asset, Current	388,188,000						388,188,000
Derivative Asset, Not offset, Policy election deduction, Current	31,606,000						31,606,000
Derivative Asset, Fair Value, Amount not offset against collateral, Current	356,582,000						356,582,000
Derivative Asset, Fair Value, Gross Asset	408,728,000						408,728,000		543,821,000
Derivative Asset, Fair Value, Gross Amount Not Offset on Balance Sheet	31,606,000						31,606,000		32,876,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	249,470,000						249,470,000		479,912,000
Derivative Liability, Fair Value, Gross Liability	284,212,000						284,212,000		513,599,000
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	3,136,000						3,136,000		811,000
Derivative Liability, Fair Value, Gross Amount Not Offset on Balance Sheet	31,606,000						31,606,000		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	25,000,000	$ 24,600,000	24,100,000				25,000,000
Embedded Derivative, Gain on Embedded Derivative	500,000	$ 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	6,663,000						6,663,000		12,364,000
Derivative Asset, Fair Value, Gross Asset	10,558,000						10,558,000		21,551,000
Derivative Asset, Fair Value, Gross Amount Not Offset on Balance Sheet	3,895,000						3,895,000		9,187,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	7,794,000						7,794,000		13,102,000
Derivative Liability, Fair Value, Gross Liability	11,689,000						11,689,000		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	3,895,000						3,895,000		9,187,000
Derivative Asset, Notional Amount	789,400,000						789,400,000		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	9,496,000						9,496,000		22,078,000
Derivative Asset, Fair Value, Gross Asset	9,496,000						9,496,000		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	1,182,000						1,182,000
Derivative Liability, Fair Value, Gross Liability	1,182,000						1,182,000
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	4,000						4,000		8,000
Derivative Liability, Fair Value, Gross Liability	4,000						4,000		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	335,916,000						335,916,000		476,503,000
Derivative Asset, Fair Value, Gross Asset	363,627,000						363,627,000		500,192,000
Derivative Asset, Fair Value, Gross Amount Not Offset on Balance Sheet	27,711,000						27,711,000		23,689,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	240,490,000						240,490,000		466,802,000
Derivative Liability, Fair Value, Gross Liability	271,337,000						271,337,000		491,302,000
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	3,136,000						3,136,000		811,000
Derivative Liability, Fair Value, Gross Amount Not Offset on Balance Sheet	27,711,000						27,711,000		$ 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							13,800,000	$ 7,600,000
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	4,507,000						4,507,000
Derivative Asset, Not offset, Policy election deduction, Current	0						0
Derivative Asset, Fair Value, Amount not offset against collateral, Current	4,507,000						4,507,000
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