Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current assets:
Trade accounts receivable, allowances for doubtful accounts	$ 1,941	$ 1,849
Other assets:
Patents, trademarks, and other intangible assets, accumulated amortization	$ 23,552	$ 22,572
Equity:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	79,808,033	79,673,374
Treasury stock, shares held	2,269,911	2,249,959