Recent Accounting Pronouncements - Lease Expense (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Sub lease income from chartered-in contracts greater than 12 months	$ 2,759,065	$ 5,841,817
Charter hire expenses
Lessee, Lease, Description [Line Items]
Lease expense for chartered-in contracts less than 12 months	7,684,182	16,044,965
Operating lease, expense	3,495,298	6,626,421
Lease cost	11,179,480	22,671,386
General and administrative expenses
Lessee, Lease, Description [Line Items]
Operating lease, expense	177,356	355,356
Voyage charters
Lessee, Lease, Description [Line Items]
Sub lease income from chartered-in contracts greater than 12 months	$ 200,000	$ 1,000,000