SEGMENT DATA (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) Segment	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
SEGMENT DATA [Abstract]
Number of reportable segments | Segment			2
Revenues [Abstract]
Marine transportation	$ 425,053	$ 456,745	$ 844,958	$ 892,516
Diesel engine services	118,103	171,309	285,871	324,784
Total revenues	543,156	628,054	1,130,829	1,217,300
Segment profit (loss)	93,072	121,679	190,974	222,679
Total assets	4,154,503		4,154,503		$ 4,141,909
Other segment disclosures [Abstract]
Gain on disposition of assets	91	527	1,646	578
Interest expense	(4,759)	(5,469)	(10,009)	(11,087)
Other income (expense)	(303)	123	(243)	(113)
Other [Member]
Revenues [Abstract]
Segment profit (loss)	(8,870)	(8,626)	(16,080)	(17,949)
Total assets	54,855		54,855		88,084
Other segment disclosures [Abstract]
General corporate expenses	(3,899)	(3,807)	(7,474)	(7,327)
Gain on disposition of assets	91	527	1,646	578
Interest expense	(4,759)	(5,469)	(10,009)	(11,087)
Other income (expense)	(303)	123	(243)	(113)
Profit (loss) from other segment	(8,870)	(8,626)	(16,080)	(17,949)
Details of "Other" total assets [Abstract]
General corporate assets	52,983		52,983		85,545
Investment in affiliates	1,872		1,872		2,539
Total other assets	54,855		54,855		88,084
Reporting Segments [Member] | Marine transportation [Member]
Revenues [Abstract]
Marine transportation	425,053	456,745	844,958	892,516
Segment profit (loss)	97,011	115,968	193,280	213,519
Total assets	3,425,973		3,425,973		3,317,696
Reporting Segments [Member] | Diesel engine services [Member]
Revenues [Abstract]
Diesel engine services	118,103	171,309	285,871	324,784
Segment profit (loss)	4,931	$ 14,337	13,774	$ 27,109
Total assets	$ 673,675		$ 673,675		$ 736,129