Vessels and vessel improvements - Schedule of Vessels and vessel improvements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Movement in Property, Plant and Equipment [Roll Forward]
Vessels and vessel improvements	$ 810,713,959
Transfer from advances paid for vessel purchases	0	$ 3,250,000	$ 0
Depreciation expense	(300,000)	(300,000)	(300,000)
Vessels and vessel improvements	908,075,913	810,713,959
Vessels and Vessel Improvements
Movement in Property, Plant and Equipment [Roll Forward]
Vessels and vessel improvements	810,713,959	835,959,084
Transfer from advances paid for vessel purchases	3,250,000	0
Purchase of vessels and vessel improvements	128,326,112	979,612
Fair value of warrants issued as consideration for vessel purchases	10,679,988	0
Sale of vessels	(4,885,998)	(23,458,118)
Advances paid for vessel installation	4,588,585	39,706,507
Depreciation expense	(44,596,733)	(42,473,126)
Vessels and vessel improvements	$ 908,075,913	$ 810,713,959	$ 835,959,084