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Landfill Accounting - Reconciliation of Company's Final Capping, Closure and Post-Closure Liability (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Accounting Policies [Line Items]
Final capping, closure and post-closure liability at December 31, 2011	$ 30,883
Adjustments to final capping, closure and post-closure liabilities	3,467
Liabilities incurred	2,072
Accretion expense	1,870	1,451
Closure payments	(17)
Assumption of closure liabilities from acquisitions	1,762
Final capping, closure and post-closure liability at September 30, 2012	$ 40,037

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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