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Derivative Instruments and Risk Management - Summary of Commodity Swaps (Parenthetical) (Detail)	Jun. 30, 2013 T	Dec. 31, 2012 T
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Commodity swaps, notional quantity	25	275

X

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

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Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

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- Details

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Data Type:	xbrli:stringItemType
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