Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Trade accounts receivable, allowance for doubtful accounts	$ 2,709	$ 2,527
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000	150,000
Common stock, shares issued	88,841	91,594
Common stock, shares outstanding	88,841	91,594