Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current assets:
Trade accounts receivable, allowances for doubtful accounts	$ 1,849	$ 2,590
Other assets:
Patents, trademarks, and other intangible assets, accumulated amortization	$ 22,572	$ 21,499
Equity:
Common stock, par value (in dollars per share)	$ 0.01
Common stock, shares authorized	100,000,000
Common stock, shares issued	79,673,374	77,825,398
Treasury stock, shares held	2,249,959	1,533,653