Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts receivable, allowance for doubtful accounts	$ 10,093	$ 9,383
Property and equipment, accumulated depreciation	$ 331,538	$ 325,595
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	206,475,743	206,392,013
Common stock, shares outstanding	206,475,743	206,392,013