RECEIVABLES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
RECEIVABLES
Trade	$ 183,747	$ 186,502
Unbilled revenue	62,029	52,858
Other	7,421	5,554
Total receivables	253,197	244,914
Allowance for credit losses	(3,043)	(2,936)	$ (3,010)
Receivables, net	250,154	241,978
Change in the allowance for doubtful accounts receivable
Balance at Beginning of Period	2,936	3,010	2,998
Charged (Credited) to Costs and Expenses	1,179	(412)	226
Recoveries (Deductions/Write-offs)	(1,075)		(439)
Recoveries		296
Adjustments	3	42	225
Balance at End of Period	$ 3,043	$ 2,936	$ 3,010