LEASES (Schedule of lease cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating lease, cost	$ 7,540	$ 13,033	$ 17,771	$ 30,218
Total lease cost	4,402	6,500	10,250	12,735
Vessel/Fleet [Member] | Charter Hire Expense [Member]
Operating lease, cost	2,977	3,432	6,705	7,089
Short-term lease, cost	1,126	2,719	2,926	4,946
Office Space [Member] | General and Administrative Expense [Member]
Operating lease, cost	257	249	506	498
Short-term lease, cost	0	29	29	58
Office Space [Member] | Voyage Expense [Member]
Operating lease, cost	42	42	84	84
Short-term lease, cost	0	26	0	52
Office Space [Member] | Vessel Expense [Member]
Short-term lease, cost	0	3	0	8
Lightering Services Component [Member] | Vessel/Fleet [Member]
Short-term lease, cost	$ 100	$ 1,800	$ 200	$ 8,400