CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 1,667	$ 1,691
Accumulated depreciation	$ 361,541,000	$ 341,119,000
Capital Stock, par value (in dollars per share)	$ 1	$ 1
Capital Stock, authorized shares (shares)	50,000,000	50,000,000
Capital Stock, shares issued (shares)	18,668,000	18,577,000
Capital Stock, shares outstanding (shares)	18,668,000	18,577,000