Vessels - Additional Information (Details)					3 Months Ended		6 Months Ended		12 Months Ended
	May 02, 2019 USD ($)	Jan. 04, 2019 USD ($)	Dec. 13, 2018 USD ($)	Aug. 14, 2018 USD ($)	Jun. 30, 2019 USD ($) vessel	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) vessel	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jan. 23, 2019 option	Dec. 21, 2018 USD ($)	Nov. 20, 2018 vessel	Sep. 04, 2018 order	Sep. 04, 2018 vessel	Sep. 04, 2018 USD ($)	Sep. 04, 2018 scrubber
Property, Plant and Equipment [Line Items]
Number of vessels | vessel					45		45
Proceeds from sale of vessels							$ 22,631,367	$ 9,719,013
Gain on sale of vessels					$ 966,802	$ 105,073	5,073,349	$ 105,073
Vessel Thrasher
Property, Plant and Equipment [Line Items]
Proceeds from sale of vessels	$ 9,800,000
Gain on sale of vessels					1,000,000		1,000,000
Vessel Merlin
Property, Plant and Equipment [Line Items]
Proceeds from sale of vessels		$ 6,100,000
Gain on sale of vessels							1,900,000
2015 Built Ultramax Vessel
Property, Plant and Equipment [Line Items]
Vessel purchase price											$ 20,400,000
Deposits on vessel purchases									$ 2,000,000
Supramax Vessels
Property, Plant and Equipment [Line Items]
Proceeds from sale of vessels			$ 6,100,000
Gain on sale of vessels							2,200,000
Scrubber Systems
Property, Plant and Equipment [Line Items]
Number of vessels | vessel														37
Number of scrubbers												15				19
Additional units to be purchased													18	18
Number of options exercised | option										3
Projected project costs															$ 2,200,000
System costs					$ 41,800,000		$ 41,800,000
Scrubber Systems | Maximum
Property, Plant and Equipment [Line Items]
Number of scrubbers | scrubber																37
Ballast Water Treatment System
Property, Plant and Equipment [Line Items]
Projected project costs				$ 500,000
Advance paid for purchase of Cape Town Eagle at December 31, 2018				$ 3,200,000