VESSELS, OTHER PROPERTY AND DEFERRED DRYDOCK (Vessels and Other Property) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property, plant and equipment, disposals	$ 35,352
Vessels and other property, less accumulated depreciation	632,509	$ 684,468
Vessel Excluding Construction In Progress [Member]
Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization, Sale or Disposal of Property, Plant and Equipment	27,287
Cost	849,713	892,022	$ 1,156,117	$ 1,156,064
Accumulated depreciation	(217,633)	(208,318)	(313,392)	(262,028)
Vessels and other property, less accumulated depreciation	632,080	683,704	842,725	$ 894,036
Impairment	(6,957)	(264,095)
Vessel additions			53
Depreciation	37,681	58,489	$ 51,364
Vessel/Fleet [Member]
Property, Plant and Equipment [Line Items]
Cost	849,713	892,022
Accumulated depreciation	(217,633)	(208,318)
Vessels and other property, less accumulated depreciation	632,080	683,704
Other Property [Member]
Property, Plant and Equipment [Line Items]
Cost	5,630	5,619
Accumulated depreciation	(5,201)	(4,855)
Vessels and other property, less accumulated depreciation	$ 429	$ 764