Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Trade accounts receivable, allowances for doubtful accounts	$ 856	$ 1,085
Other assets:
Patents, trademarks, and other intangible assets, accumulated amortization	$ 30,223	$ 27,044
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	81,215,135	80,446,169
Treasury stock, shares held	2,434,482	2,334,137