Recent Accounting Pronouncements - Future Minimum Lease Payments (Details) - USD ($)	Jun. 30, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Discount rate upon adoption	5.48%
Six months ending December 31, 2019	$ 7,435,125
2020	10,601,605
2021	6,525,967
2022	483,048
2023	244,878
Operating lease payments	25,290,623
Operating lease, liability	23,944,324
Lease liabilities - short term	12,155,767	$ 14,495,352
Noncurrent portion of operating lease liabilities	11,788,557	16,027,764
Discount based on incremental borrowing rate	$ 1,346,299
Chartered-in contracts greater than 12 months
Lessee, Lease, Description [Line Items]
Discount rate upon adoption	5.37%
Six months ending December 31, 2019	$ 7,070,784
2020	9,867,731
2021	5,825,710
2022	0
2023	0
Operating lease payments	22,764,225
Operating lease, liability	21,676,741
Lease liabilities - short term	11,547,210	13,802,149
Noncurrent portion of operating lease liabilities	10,129,531	14,160,374
Discount based on incremental borrowing rate	$ 1,087,484
Office leases
Lessee, Lease, Description [Line Items]
Discount rate upon adoption	5.80%
Six months ending December 31, 2019	$ 364,341
2020	733,874
2021	700,257
2022	483,048
2023	244,878
Operating lease payments	2,526,398
Operating lease, liability	2,267,583
Lease liabilities - short term	608,557	693,203
Noncurrent portion of operating lease liabilities	1,659,026	$ 1,867,390
Discount based on incremental borrowing rate	$ 258,815