CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Trade accounts receivable, allowances	$ 1,652	$ 1,820	$ 1,819
Treasury stock, shares	90,000	88,000	88,000
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	39,233,000	38,544,000	38,645,000
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	26,302,000	25,584,000	25,605,000