CONSOLIDATED STATEMENTS OF Financial Position (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Trade accounts receivable, allowances	$ 2,224	$ 2,225	$ 1,976
Treasury stock, shares	83,000	80,000	80,000
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	38,283,000	37,382,000	38,257,000
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	24,245,000	23,542,000	23,571,000