PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Participation in Multi-Employer Pension Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions made by the Company	$ 2,795	$ 2,855	$ 2,714
American Maritime Officers Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
EIN / Pension Plan Number	13-1936709
Rehabilitation Plan Status	Implemented
Contributions made by the Company	$ 984	1,015	1,001
Marine Engineers Beneficial Association Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
EIN / Pension Plan Number	51-6029896
Contributions made by the Company	$ 1,411	1,406	1,286
Seafarers Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
EIN / Pension Plan Number	13-6100329
Contributions made by the Company	$ 400	$ 434	$ 427