Vessels - Vessel and Vessel Improvements (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Movement in Property, Plant and Equipment [Roll Forward]
Vessels and vessel improvements, beginning balance	$ 682,944,936
Vessels and vessel improvements, ending balance	695,343,213	$ 682,944,936
Vessels and Vessel Improvements
Movement in Property, Plant and Equipment [Roll Forward]
Vessels and vessel improvements, beginning balance	682,944,936
Advance paid for purchase of Cape Town Eagle at December 31, 2018		2,040,000
Purchase of Vessels and Vessel Improvements	18,465,609
Vessel depreciation expense	(8,107,332)
Vessels and vessel improvements, ending balance	$ 695,343,213	$ 682,944,936