Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts receivable, allowance for doubtful accounts	$ 9,167	$ 10,381
Property and equipment, accumulated depreciation	$ 317,896	$ 296,481
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	208,950,205	212,003,662
Common stock, shares outstanding	208,950,205	212,003,662