Vessels and vessel improvements - Schedule of Vessels and vessel improvements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Movement in Property, Plant and Equipment [Roll Forward]
Vessel and vessel improvements at the beginning of the year	$ 567,592,950
Vessels and Vessel Improvements, at December 31, 2017	690,236,419	$ 567,592,950
Vessels and Vessel Improvements
Movement in Property, Plant and Equipment [Roll Forward]
Vessel and vessel improvements at the beginning of the year	567,592,950	733,960,731
Advance paid for purchase of Singapore Eagle at December 31, 2016	1,926,886	0
Purchase of Vessels and vessel improvements	174,400,746	19,860,401
Disposal of Vessels	(15,218,633)	(13,102,860)
Reclassification to vessels held for sale	(9,316,095)	(8,688,601)
Depreciation Expense	(29,149,435)	(35,408,859)
Vessel impairment charge	0	(129,027,862)
Vessels and Vessel Improvements, at December 31, 2017	$ 690,236,419	$ 567,592,950