ACCOUNTS RECEIVABLE (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts	$ (5,000)	$ (5,000)
Accounts Receivable, Net	172,367	137,932
Customer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	99,000	81,000
Customer | Customer, Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	45,000	39,000
Customer | Due from Affiliates
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	8,000	7,000
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	25,000	16,000
Derivatives | Customer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross	$ 8,000	$ 9,000