RECEIVABLES (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Receivables [Abstract]
Trade accounts receivable		$ 205,081	$ 207,266
Unbilled receivables		74,454	76,268
Allowance for doubtful accounts		(14,431)	(15,182)
Total	[1]	$ 265,104	$ 268,352

[1] Includes billed and unbilled amounts, net of allowance for doubtful accounts. See Note 3 for details.