VESSELS, OTHER PROPERTY AND DEFERRED DRYDOCK (Vessel Activity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Vessel Cost
Disposals	$ (35,352)
Net Book Value
Beginning Balance	684,468
Ending Balance	632,509	$ 684,468
Vessel/Fleet [Member]
Vessel Cost
Beginning Balance	892,022
Ending Balance	849,713	892,022
Accumulated Depreciation
Beginning Balance	(208,318)
Ending Balance	(217,633)	(208,318)
Net Book Value
Beginning Balance	683,704
Ending Balance	632,080	683,704
Vessel Excluding Construction In Progress [Member]
Vessel Cost
Beginning Balance	892,022	1,156,117	$ 1,156,064
Purchases and vessel additions			53
Impairment	(6,957)	(264,095)
Ending Balance	849,713	892,022	1,156,117
Accumulated Depreciation
Beginning Balance	(208,318)	(313,392)	(262,028)
Depreciation	(37,681)	(58,489)	(51,364)
Impairment	1,079	163,563
Disposals	27,287
Ending Balance	(217,633)	(208,318)	(313,392)
Net Book Value
Beginning Balance	683,704	842,725	894,036
Ending Balance	$ 632,080	$ 683,704	$ 842,725