CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Trade accounts receivable, allowance	$ 4,596	$ 8,882
Preferred stock, authorized shares (in shares)	15,000,000	15,000,000
Preferred stock, outstanding shares (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	240,000,000	240,000,000
Common stock, issued shares (in shares)	81,711,000	81,306,000
Treasury stock, shares (in shares)	2,890,000	2,912,000