CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Trade accounts receivables, allowance for doubtful accounts	$ 4,460	$ 10,425
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	105,616,000	110,547,000
Common stock, shares outstanding	105,616,000	110,547,000