CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Allowance for accounts receivable	$ 11,507	$ 11,606
Accumulated depreciation on Property, plant and equipment	$ 390,569	$ 385,472
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares outstanding	49,207,444	49,144,212
Treasury stock, shares	10,933,185	10,932,361