Condolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Allowance for doubtful accounts	$ 3,036	$ 2,898
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	58,901,385	58,593,802
Treasury stock, at cost	4,680,118	4,254,350