Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Per Share data	Jun. 30, 2011	Dec. 31, 2010
Current Assets:
Allowance for doubtful accounts receivable	$ 20,918	$ 29,798
Accumulated depreciation of property and equipment	$ 569,684	$ 516,565
Stockholders' Equity:
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000	200,000
Common Stock, Shares Issued	139,776	116,336
Common Stock, Shares Outstanding	137,880	114,784
Treasury stock, shares	1,896	1,552