Schedule of Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Property, Plant, and Equipment Disclosure [Line Items]
Purchased and internally developed software	$ 83,239	$ 73,561
Portable People Meter equipment	45,570	49,601
Computer equipment	23,793	21,776
Leasehold improvements	18,780	17,833
Machinery, furniture and fixtures	9,218	8,598
Property and equipment, gross	180,600	171,369
Accumulated depreciation and amortization	(118,931)	(100,718)
Property and equipment, net	$ 61,669	$ 70,651

The cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement.

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Gross amount of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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- Definition

Amount, net of accumulated depreciation, depletion and amortization, of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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