Enterprise-Wide Information (Schedule Of Revenues For Each Group Of Services Provided To External Customers) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Enterprise Wide Revenue By Type/Geography [Line Items]
Service Revenues	$ 422,310	$ 395,379	$ 384,952
Radio Audience Ratings Services [Member]
Enterprise Wide Revenue By Type/Geography [Line Items]
Service Revenues	340,479	317,606	307,217
Local Market Consumer Information Services [Member]
Enterprise Wide Revenue By Type/Geography [Line Items]
Service Revenues	35,173	35,187	34,991
Software Applications [Member]
Enterprise Wide Revenue By Type/Geography [Line Items]
Service Revenues	35,676	34,138	33,809
All Other Services [Member]
Enterprise Wide Revenue By Type/Geography [Line Items]
Service Revenues	$ 10,982	$ 8,448	$ 8,935