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MARGIN ACCOUNTS, DERIVATIVES AND FAIR VALUE MEASURES - Fuel Swap Contracts (Details) - Fuel swap contracts - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 3,543,000	$ 74,000
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Net Asset (Liability)		377,273
Recurring | Fuel
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Net Asset (Liability)	$ (3,165,967)	$ 377,000

X

- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

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- Definition

Fair value of asset after deduction of liability.

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