Recent Accounting Pronouncements - Lease Expense (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lessee, Lease, Description [Line Items]
Sublease income from chartered-in contracts greater than 12 months *	$ 5,607,346	$ 1,292,814	$ 6,753,137	$ 5,290,038
Charter hire expenses
Lessee, Lease, Description [Line Items]
Lease expense for chartered-in contracts less than 12 months	3,157,702	1,644,173	8,644,466	4,389,586
Operating lease, expense	3,011,842	3,075,194	6,005,298	6,370,720
Lease cost	6,169,544	4,719,367	14,649,764	10,760,306
General and administrative expenses
Lessee, Lease, Description [Line Items]
Operating lease, expense	$ 92,383	$ 181,412	$ 276,389	$ 362,824