Other Non-Current Liabilities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011
Other Liabilities [Line Items]
Unfavorable storage contracts, amount recognized as revenue	$ 7.6
2012
Other Liabilities [Line Items]
Unfavorable storage contracts, revenue expected to be recognized	11.0
2013
Other Liabilities [Line Items]
Unfavorable storage contracts, revenue expected to be recognized	11.0
2014
Other Liabilities [Line Items]
Unfavorable storage contracts, revenue expected to be recognized	11.1
2015
Other Liabilities [Line Items]
Unfavorable storage contracts, revenue expected to be recognized	11.1
2016
Other Liabilities [Line Items]
Unfavorable storage contracts, accelerated amortization	$ 6.0

Amount of previously reported deferred or unearned revenue that was recognized as revenue during the period. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 13

-Section A

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 605

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 13.A.4(a).Q1)

-URI http://asc.fasb.org/extlink&oid=6600647&loc=d3e214044-122780

Name:	us-gaap_DeferredRevenueRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration