Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts receivable, allowance for doubtful accounts	$ 10,187	$ 9,383
Property and equipment, accumulated depreciation	$ 337,154	$ 325,595
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	205,455,991	206,392,013
Common stock, shares outstanding	205,455,991	206,392,013