Recent Accounting Pronouncements - Operating Lease Assets and Liabilities (Details) - USD ($)	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 22,462,057	$ 28,705,002
Current portion of operating lease liabilities	12,155,767	14,495,352
Noncurrent portion of operating lease liabilities	11,788,557	16,027,764
Fair value below contract value of time charters acquired	$ 0		$ 1,818,114
Discount rate	5.48%
Minimum
Lessee, Lease, Description [Line Items]
Discount rate	5.05%
Maximum
Lessee, Lease, Description [Line Items]
Discount rate	6.08%
Weighted Average
Lessee, Lease, Description [Line Items]
Discount rate	5.49%
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		28,700,000
Fair value below contract value of time charters acquired		1,800,000
Chartered-in contracts greater than 12 months
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 20,194,474	26,144,409
Current portion of operating lease liabilities	11,547,210	13,802,149
Noncurrent portion of operating lease liabilities	$ 10,129,531	14,160,374
Discount rate	5.37%
Office leases
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 2,267,583	2,560,593
Current portion of operating lease liabilities	608,557	693,203
Noncurrent portion of operating lease liabilities	$ 1,659,026	$ 1,867,390
Discount rate	5.80%