Consolidated Balance Sheets (unaudited) (Parenthetical) (USD $) In Thousands, except Share data	Sep. 30, 2011	Dec. 31, 2010
Current assets:
Allowance for doubtful accounts	$ 1,717	$ 1,525
Accumulated depreciation	$ 107,938	$ 105,342
Stockholders' equity:
Common stock, par value (in dollars per share)	$ 0.008	$ 0.008
Common stock, shares authorized (in shares)	40,000,000	40,000,000
Common stock, issued (in shares)	30,684,172	30,506,252
Common stock, shares outstanding (in shares)	25,627,504	25,761,334
Treasury stock, shares of common stock (in shares)	5,056,668	4,744,918