Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Receivables, allowance for doubtful accounts	$ 9,979	$ 9,159
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	160,000,000	160,000,000
Common stock, shares issued	95,345,362	95,345,362
Common stock, shares outstanding	58,277,646	59,583,770
Treasury stock, shares	37,067,716	35,761,592