Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 3,806	$ 3,266
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	109,116,622	109,487,979