CONSOLIDATED STATEMENTS OF Financial Position (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Trade accounts receivable, allowances	$ 1,944	$ 1,884	$ 2,038
Treasury stock, shares	85,000	83,000	83,000
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	38,319,000	37,701,000	38,231,000
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	24,918,000	24,221,000	24,227,000