SEGMENT DATA (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) Segment	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
SEGMENT DATA [Abstract]
Number of reportable segments | Segment	2
Revenues [Abstract]
Marine transportation	$ 343,652	$ 378,343
Diesel engine services	148,053	80,390
Total revenues	491,705	458,733
Segment profit (loss)	40,998	61,343
Total assets	4,257,292		$ 4,289,895
Other segment disclosures [Abstract]
Gain on disposition of assets	99	67
Interest expense	(4,457)	(4,193)
Other income (expense)	(116)	135
Reporting Segments [Member] | Marine Transportation [Member]
Revenues [Abstract]
Marine transportation	343,652	378,343
Segment profit (loss)	35,254	69,795
Total assets	3,571,254		3,613,951
Reporting Segments [Member] | Diesel Engine Services [Member]
Revenues [Abstract]
Diesel engine services	148,053	80,390
Segment profit (loss)	13,734	(806)
Total assets	636,758		623,268
Intersegment Eliminations [Member] | Marine Transportation [Member]
Revenues [Abstract]
Total revenues	5,430	4,384
Segment profit (loss)	543	438
Other [Member]
Revenues [Abstract]
Segment profit (loss)	(7,990)	(7,646)
Total assets	49,280		52,676
Other segment disclosures [Abstract]
General corporate expenses	(3,516)	(3,655)
Gain on disposition of assets	99	67
Interest expense	(4,457)	(4,193)
Other income (expense)	(116)	135
Loss from other segment	(7,990)	$ (7,646)
Details of "Other" total assets [Abstract]
General corporate assets	47,593		50,054
Investment in affiliates	1,687		2,622
Total other assets	$ 49,280		$ 52,676