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Derivative Financial Instruments and Fair Value and Credit Risk of Financial Instruments - Additional information (Detail) (USD $) In Millions, unless otherwise specified | 1 Months Ended | 6 Months Ended | 12 Months Ended
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Aug. 31, 2012 bbl | Dec. 31, 2010 | Dec. 31, 2012 bbl | Dec. 31, 2011 | Jun. 30, 2010
Derivative [Line Items] |  |  |  |  |
Unrealized loss, included in Accumulated other comprehensive income/loss |  |  | $ 1.3 | $ (0.5) |
Percentage of assets classified within level 3 of fair value hierarchy to total assets and liabilities measured at fair value |  |  | 1.00% |  |
Commodity Contract |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
LME copper prices, average (per ton) | 118.90 | 7,828.00 | 7,951.00 | 8,836.00 | 6,651.00
LME copper prices, average provisional price (per ton) |  |  | 7,322 |  |
Applicable forward copper price |  |  | 7,930 |  |
Commodity contract, volume | 10,000 |  |  |  |
Commodity contract outstanding,volume |  |  | 20,000 |  |
Commodity contract, mark-to-market value |  |  | 0.1 |  |
Commodity Contract | Sales |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Gain (loss) on mark-to-market value of contracts |  |  | $ 15.6 | $ 20.6 |

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- Definition Commodity average price + References No definition available. + Details
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- Definition Commodity average provisional price + References No definition available. + Details
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- Definition Percentage of unobservable assets to total financial instruments measured at fair value + References No definition available. + Details
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- Definition Volume Of Commodity Outstanding + References No definition available. + Details
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- Definition Volume of Commodity Sold + References No definition available. + Details
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- Definition The average forward price on the group of price risk forward or futures contracts, such as gas futures contracts. + References No definition available. + Details
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- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611 + Details
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- Definition Net Increase or Decrease in the fair value of the derivative or group of derivatives included in earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 + Details
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- Definition Amount of gain (loss) recognized in other comprehensive income, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1a) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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