Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jul. 01, 2012	Dec. 31, 2011
Condensed Consolidated Balance Sheets [Abstract]
Allowance for doubtful debts	$ 1,116	$ 1,100
Accumulated depreciation on property, plant and equipment	$ 241,634	$ 241,585
Preferred stock, without par value
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares issued
Common stock, without par value
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	55,208,565	54,790,110
Common stock held in treasury, shares	21,296,593	20,724,106