Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Condensed Consolidated Balance Sheets
Allowance for doubtful accounts receivable	$ 4,984	$ 4,716	$ 4,996
Allowance for credit losses	834	971	1,148
Fixed assets, accumulated depreciation and amortization	155,428	147,280	138,691
Goodwill and other intangible assets, accumulated amortization	$ 6,532	$ 5,846	$ 5,193
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000	200,000,000
Common stock, shares issued	67,553,008	67,320,667	67,007,643
Common stock, shares outstanding	67,553,008	67,320,667	67,007,643