Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Trade accounts receivable, allowances	$ 5,869	$ 5,934
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	87,556,248	87,519,715
Common stock, shares outstanding	69,203,967	69,883,808
Treasury stock, shares	18,352,281	17,635,907