Goodwill and Other Intangible Assets Schedule of Goodwill (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Goodwill [Roll Forward]
Balance as of January 1, 2013 (1)	$ 723,701	[1]
Divestiture of Advertising Decision Solutions business	(1,939)
Acquisition of strategic network assets	29,509
Balance as of September 30, 2013	$ 751,271

[1] Balance as of January 1, 2013 has been revised to reflect purchase accounting measurement period adjustments (Note 6).