Consolidated Balance Sheets Parenthetical Parentheticals (USD $) In Thousands, except Share data	Jun. 30, 2011	Dec. 31, 2010
Allowance for doubtful accounts	$ 5,724	$ 4,925
Accumulated depreciation	$ 804,006	$ 731,453
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	4,500,000	4,500,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	48,426,816	48,408,259
Common stock, shares outstanding	48,426,816	48,408,259