Arbitron Mobile Contingent Consideration - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	6 Months Ended		12 Months Ended
	Jul. 28, 2011	Jun. 30, 2013 Y	Jun. 30, 2013 Noncurrent Liabilities	Dec. 31, 2012 Noncurrent Liabilities	Jun. 30, 2013 Maximum
Business Acquisition, Contingent Consideration [Line Items]
Business acquisition, cash paid	$ 10.6
Fair value of contingent consideration			0.6	0.6
Potential cash payment to shareholders					$ 12.0
Contingent consideration expiration year		2015
Period for performance evaluation, years		4
Business acquisition, effective date		Jul. 28, 2011