Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data	Jun. 30, 2011	Dec. 31, 2010
Condensed Consolidated Balance Sheets
Allowance for doubtful accounts	$ 12,052	$ 11,531
Accumulated depreciation on property, plant and equipment	$ 362,198	$ 338,010
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares outstanding	52,315,578	52,181,335
Treasury stock, shares	7,344,984	7,268,653