Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Assets:
Current derivatives	$ 18,336	$ 16,818
Derivative assets, noncurrent	1,508	3,889
Liabilities:
Commodity derivative liabilities - current		(388)
Fair Value, Measurements, Recurring
Assets:
Publicly traded equity securities	3,674	6,440
Liabilities:
Deferred compensation - noncurrent liability	(3,802)	(6,948)
Totals	19,716	19,811
Fair Value, Measurements, Recurring \| Commodity contracts
Assets:
Current derivatives	18,336	15,075
Derivative assets, noncurrent	1,508	3,042
Liabilities:
Commodity derivative liabilities - current		(388)
Fair Value, Measurements, Recurring \| Commodity contracts \| Fair Value, Inputs, Level 2
Assets:
Current derivatives	18,336	15,075
Derivative assets, noncurrent	1,508	3,042
Liabilities:
Commodity derivative liabilities - current		(388)
Fair Value, Measurements, Recurring \| Interest rate swaps
Assets:
Current derivatives		1,743
Derivative assets, noncurrent		847
Fair Value, Measurements, Recurring \| Interest rate swaps \| Fair Value, Inputs, Level 2
Assets:
Current derivatives		1,743
Derivative assets, noncurrent		847
Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 1
Assets:
Publicly traded equity securities	3,674	6,440
Liabilities:
Deferred compensation - noncurrent liability	(3,802)	(6,948)
Totals	(128)	(508)
Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 2
Liabilities:
Totals	$ 19,844	$ 20,319

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, 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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+ Details

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents investment securities as of the balance sheet date which may include marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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