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Asset retirement obligation (Details) (CAD)	12 Months Ended
Asset retirement obligation (Details) (CAD)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Asset Retirement Obligation Details
Asset retirement obligation, beginning of the year	57,953	54,444	51,254
Accretion expense	3,860	3,509	4,092
Costs incurred			(902)
Asset retirement obligation, end of the year	61,813	57,953	54,444

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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