CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Mar. 30, 2013	Dec. 31, 2012	Mar. 31, 2012
Trade accounts receivable, allowances	$ 2,187	$ 2,142	$ 1,618
Treasury stock, shares	76	73	73
Common stock
Common stock, par value (in dollars per share)	$ 0.6944	$ 0.6944	$ 0.6944
Common stock, shares authorized	120,000	120,000	120,000
Common stock, shares issued	37,593	36,649	37,390
Class B common stock
Common stock, par value (in dollars per share)	$ 0.6944	$ 0.6944	$ 0.6944
Common stock, shares authorized	40,000	40,000	40,000
Common stock, shares issued	22,263	21,627	21,652