CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Mar. 29, 2014	Dec. 31, 2013	Mar. 30, 2013
Trade accounts receivable, allowances	$ 2,068	$ 2,042	$ 2,187
Treasury stock, shares	78	76	76
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	37,861	37,011	37,593
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	22,915	22,256	22,263