CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 28, 2013	Dec. 31, 2012	Sep. 29, 2012
Trade accounts receivable, allowances	$ 3,446	$ 2,142	$ 3,501
Treasury stock, shares	76,000	73,000	73,000
Common stock
Common stock, par value (in dollars per share)	$ 0.6944	$ 0.6944	$ 0.6944
Common stock, shares authorized	120,000,000	120,000,000	120,000,000
Common stock, shares issued	37,376,000	36,649,000	36,998,000
Class B common stock
Common stock, par value (in dollars per share)	$ 0.6944	$ 0.6944	$ 0.6944
Common stock, shares authorized	40,000,000	40,000,000	40,000,000
Common stock, shares issued	22,259,000	21,627,000	21,629,000