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Reconciliation of Final Capping, Closure and Post-Closure Liability Balance (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Reconciliation of Changes in Asset Retirement Obligations [Line Items]
Final capping, closure and post-closure liability at December 31, 2012	$ 46,473
Adjustments to final capping, closure and post-closure liabilities	(3,081)
Liabilities incurred	852
Accretion expense associated with landfill obligations	707	612
Final capping, closure and post-closure liability at March 31, 2013	$ 44,951

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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