CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Trade accounts receivable, net of allowances of $6,969 and $6,319	$ 6,969	$ 6,319
Preferred stock, authorized shares (in shares)	15,000,000	15,000,000
Preferred stock, outstanding (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, shares issued (in shares)	81,301,000	77,666,000
Treasury stock, shares (in shares)	2,916,000	2,946,000