Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Per Share data	Sep. 30, 2011	Dec. 31, 2010
Current assets:
Allowance for doubtful accounts receivable	$ 18,810	$ 17,540
Accumulated depreciation of property and equipment	203,342	183,809
Accumulated amortization on intangible assets	$ 62,382	$ 50,755
Stockholders' equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	3,000	3,000
Preferred stock, shares issued
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000	100,000
Common stock, shares issued	43,875	46,325
Common stock, shares outstanding	43,875	46,325