Other Accrued Liabilities (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Other Accrued Liabilities [Line Items]
Other accrued liabilities	$ 11,810,366	$ 11,545,447
Vessel and voyage expenses
Other Accrued Liabilities [Line Items]
Other accrued liabilities	5,373,389	6,986,486
General and administrative expenses
Other Accrued Liabilities [Line Items]
Other accrued liabilities	6,050,078	3,446,113
Other expenses
Other Accrued Liabilities [Line Items]
Other accrued liabilities	$ 386,899	$ 1,112,848