Fair Value of Derivative Instruments on Condensed Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 18,987	$ 16,818
Derivative assets, noncurrent		3,889
Derivative assets	18,987	20,707
Derivative liabilities, current	3,549	388
Derivative liabilities, noncurrent	6,850
Derivative liabilities	10,399	388
Commodity contracts
Derivatives, Fair Value [Line Items]
Derivative assets	19,000
Commodity contracts \| Derivative assets/liabilities - current
Derivatives, Fair Value [Line Items]
Derivative assets, current	18,987	15,075
Derivative liabilities, current	3,549	388
Commodity contracts \| Derivative assets/liabilities - noncurrent
Derivatives, Fair Value [Line Items]
Derivative assets, noncurrent		3,042
Derivative liabilities, noncurrent	6,850
Interest rate contracts \| Derivative assets/liabilities - current
Derivatives, Fair Value [Line Items]
Derivative assets, current		1,743
Interest rate contracts \| Derivative assets/liabilities - noncurrent
Derivatives, Fair Value [Line Items]
Derivative assets, noncurrent		$ 847

Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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Fair values as of the balance sheet date for all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments and which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer, net of the effects of master netting arrangements.

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments which are expected to exist longer than one year or beyond the normal operating cycle, if longer, net of the effects of master netting arrangements.

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Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

+ References+ Details

- Definition

Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and which are expected to be extinguished or otherwise disposed of within a year or the normal operating cycle, if longer, net of the effects of master netting arrangements.

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Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and which are expected to be extinguished or otherwise disposed of after one year or beyond the normal operating cycle, if longer, net of the effects of master netting arrangements.

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