RECEIVABLES (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
Receivables [Abstract]
Trade accounts receivable		$ 142,841	$ 157,513
Unbilled receivables		60,404	46,471
Allowance for credit losses		(9,031)	(9,918)
Total	[1]	$ 194,214	$ 194,066

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