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Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions		12 Months Ended
	Jun. 30, 2011	Dec. 31, 2010 Legal Reserve	Dec. 31, 2010 Sales and Use Tax Audit
Loss Contingencies [Line Items]
Reserve established for contingency matters		$ 0.9	$ 0.5
Recorded AROs attributable to the plugging of abandoned wells	$ 7.3

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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