ACCOUNTS RECEIVABLE (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts	$ (5,000)	$ (5,000)
Accounts Receivable, Net	137,932	124,934
Customer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	81,000	74,000
Customer | Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	39,000	34,000
Customer | Due from Affiliates (Note 5)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	7,000	9,000
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	$ 16,000	$ 13,000