Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Condensed Consolidated Balance Sheets [Abstract]
Allowance for accounts receivable	$ 11,523	$ 11,485
Accumulated depreciation on property, plant and equipment	$ 361,487	$ 354,178
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares outstanding	50,608,581	50,650,971
Treasury stock, shares	9,259,557	9,122,204