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summary of activity for asset retirement obligations (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Asset retirement obligations, beginning of period	$ 55,316	$ 52,558
Accretion expense	2,216	2,758
Asset retirement obligations, end of period	57,532	55,316
Less: current portion
Long-term asset retirement obligations, end of period	$ 57,532	$ 55,316

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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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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