CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Allowance for doubtful accounts receivable	$ 39,232	$ 22,015
Stockholders' Equity
Preferred stock, par value per share	$ 100	$ 100
Preferred stock, shares authorized	100,000	100,000
Preferred stock, shares issued	0	0
Common stock, par value per share	$ 1.00	$ 1.00
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	256,992,261	256,537,535
Treasury Stock, shares	102,168,868	101,109,186