Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Consolidated Balance Sheets
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 10,372	$ 11,113
Class A Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Class A Common Stock, shares authorized	500,000,000	500,000,000
Class A Common Stock, shares issued	159,857,738	163,122,474
Class A Common Stock, shares outstanding	159,857,738	163,122,474