CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Allowance for accounts receivable	$ 11,318	$ 11,485
Accumulated depreciation on property, plant and equipment	$ 381,446	$ 354,178
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares outstanding	49,099,237	50,650,971
Treasury stock, shares	10,928,282	9,122,204