Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accounts receivable, allowance for doubtful accounts	$ 8,695	$ 8,482
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	202,553,220	206,392,013
Common stock, outstanding	202,553,220	206,392,013