Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Accounts receivable, allowance for doubtful accounts	$ 7,550	$ 8,695
Property and equipment, accumulated depreciation	$ 366,800	$ 348,282
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	195,036,823	202,553,220
Common stock, shares outstanding	195,036,823	202,553,220