Fair Value Measurements - Narrative (Details) - CF Nitrogen LLC [Member] $ in Millions	3 Months Ended
Nov. 30, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Embedded derivative asset	$ 24.1
Payments For Credit Rating Decrease In Investment	$ 5.0

Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as an asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624163-113959

Name:	us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant