CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 28, 2014	Dec. 31, 2013	Jun. 29, 2013
Trade accounts receivable, allowances	$ 1,806	$ 2,042	$ 1,907
Treasury stock, shares	78,000	76,000	76,000
Common Class A [Member]
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	37,777,000	37,011,000	37,401,000
Common Class B [Member]
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	22,910,000	22,256,000	22,261,000