Recent Accounting Pronouncements - Lease Expense (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Sub lease income from chartered-in contracts greater than 12 months *	$ 1,292,814	$ 2,759,065	$ 5,290,038	$ 5,841,817
Charter hire expenses
Lessee, Lease, Description [Line Items]
Lease expense for chartered-in contracts less than 12 months	1,644,173	7,684,182	4,389,586	16,044,965
Operating lease, expense	3,075,194	3,495,298	6,370,720	6,626,421
Lease cost	4,719,367	11,179,480	10,760,306	22,671,386
General and administrative expenses
Lessee, Lease, Description [Line Items]
Operating lease, expense	$ 181,412	$ 177,356	$ 362,824	$ 355,356