Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 3,661	$ 3,090
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, Authorized shares	800,000,000	800,000,000
Common stock, Issued shares	324,418,632	324,418,632
Treasury stock, shares	108,133,345	108,660,002