Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Supply Commitment [Line Items]
Industry fee to be credited in equal annual installments	$ 75.0
Industry fee refund for fees previously paid	70.5
Industry fee refund full credit recognized for fees previously paid	8.3
Arbitron
Supply Commitment [Line Items]
Remaining aggregate obligation under the agreements with Arbitron	$ 196.0