Vessels - Vessel and Vessel Improvements (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Movement in Property, Plant and Equipment [Roll Forward]
Vessels and vessel improvements, beginning balance	$ 690,236,419
Vessels and vessel improvements, ending balance	693,895,309	$ 690,236,419
Vessels and Vessel Improvements
Movement in Property, Plant and Equipment [Roll Forward]
Vessels and vessel improvements, beginning balance	690,236,419
Advance paid for purchase of New London Eagle at December 31, 2017		2,201,773
Purchase of Vessels and Vessel Improvements	19,841,535
Transfer to Vessels held for sale	(10,354,855)
Vessel depreciation expense	(8,029,563)
Vessels and vessel improvements, ending balance	$ 693,895,309	$ 690,236,419