FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of outstanding debt	$ 1,410,192	$ 984,017
Carrying amount of debt	1,423,294	992,406
Vessels [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair market value of assets	$ 9,850	$ 12,550