Significant Customers and Concentration of Credit Risk - Additional Information (Detail)	12 Months Ended
Dec. 31, 2012 Customer	Dec. 31, 2011 Customer	Dec. 31, 2010
Concentration Risk [Line Items]
Percentage of quantitative radio ratings services and related software to total revenue	88.00%	88.00%	88.00%
Number of customer accounting for more than ten percent of accounts receivable	1	2
Customer One
Concentration Risk [Line Items]
Percentage of accounts receivable from one customer out of total accounts receivable	26.00%	23.00%
Customer Two
Concentration Risk [Line Items]
Percentage of accounts receivable from one customer out of total accounts receivable		11.00%
Customer Concentration Risk
Concentration Risk [Line Items]
Percentage of revenue from one customer out of total revenue	20.00%	19.00%	20.00%
Number of customer accounting for more than ten percent of revenue		1

Number Of Customers That Accounted For More Than Ten Percent Of Revenue During Period

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Number Of Individual Customers Accounting For More Than Ten Percent Of Accounts Receivable

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Percentage of accounts receivable from one customer out of total accounts receivable

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Disclosure of concentration risk related to customers having 10% or more of the entity's revenue.

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Quantitative radio audience ratings and related software licensing to total revenue, percentage.

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