RECEIVABLES (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Receivables [Abstract]
Trade accounts receivable		$ 178,745	$ 207,266
Unbilled receivables		97,342	76,268
Allowance for doubtful accounts		(12,582)	(15,182)
Total	[1]	$ 263,505	$ 268,352

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