Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts receivable, allowance for doubtful accounts	$ 9,383	$ 10,381
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, authorized	2,000,000	2,000,000
Preferred stock, issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	640,000,000	640,000,000
Common stock, issued	206,392,013	212,003,662
Common stock, outstanding	206,392,013	212,003,662