SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue and Voyage Expense (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 USD ($)	Dec. 31, 2018 item
Voyage expense recognition
Net (loss) gain on purchase and sale of bunker fuel and net realizable value adjustments	$ (497)	$ 1,020	$ (734)	$ 2,909
Charter hire expenses	$ 5,475	$ 723	$ 12,743	$ 1,231
Number of vessels in vessel pools | item	0		0		0