CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 29, 2013	Dec. 31, 2012	Jun. 30, 2012
Trade accounts receivable, allowances	$ 1,907	$ 2,142	$ 1,502
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	37,401	36,649	37,273
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	22,261	21,627	21,641