Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts receivable, allowance for doubtful accounts	$ 7,369	$ 7,119
Property and equipment, accumulated depreciation	$ 381,393	$ 371,756
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	189,117,916	191,655,690
Common stock, shares outstanding	189,117,916	191,655,690