Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Class A common stock	Dec. 31, 2013 Class A common stock	Mar. 31, 2014 Class B common stock	Dec. 31, 2013 Class B common stock	Mar. 31, 2014 Class C common stock	Dec. 31, 2013 Class C common stock
Condensed Financial Statements, Captions [Line Items]
Allowance for doubtful accounts	$ 5,413	$ 5,306
Treasury stock, shares	25,104,268	24,205,200
Common stock, par value (in dollars per share)			$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized			750,000,000	750,000,000	600,000,000	600,000,000	644,871	644,871
Common stock, shares issued			238,817,762	222,399,019	3,315,238	15,424,944	644,871	644,871
Common stock, shares outstanding			213,713,494	198,193,819	3,315,238	15,424,944	644,871	644,871