Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data	Mar. 31, 2011	Dec. 31, 2010
Current assets
Net of allowance for doubtful accounts	$ 31,366	$ 30,112
Stockholders' equity
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000	10,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000	100,000
Common stock, shares issued	45,812	45,811
Common stock, shares outstanding	44,817	45,761
Treasury stock, shares outstanding	995	50