Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Consolidated Balance Sheets
Receivables, allowance for doubtful accounts	$ 11,298	$ 10,820
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	58,491,263	58,171,059
Treasury stock, shares	36,854,099	37,174,303