Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets:
Trade accounts receivable, allowance for doubtful accounts	$ 2,052	$ 1,926
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, shares issued (in shares)	31,172,666	30,766,517
Common stock, shares outstanding (in shares)	26,113,544	25,703,125
Treasury stock, shares of common stock (in shares)	5,059,122	5,063,392