Vessels - Additional Information (Details)					3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 18, 2019 USD ($)	May 02, 2019 USD ($)	Jan. 04, 2019 USD ($)	Dec. 13, 2018 USD ($)	Sep. 30, 2019 USD ($) vessel	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) vessel	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jan. 23, 2019 option	Dec. 21, 2018 USD ($)	Nov. 20, 2018 vessel	Sep. 04, 2018 vessel	Sep. 04, 2018 USD ($)	Sep. 04, 2018 scrubber	Aug. 14, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Number of vessels | vessel					47		47
Proceeds from sale of vessels							$ 29,626,659	$ 20,545,202
Gain on sale of vessels					$ 971,129	$ 235,695	6,044,479	340,768
Amount recorded in balance sheet							$ 50,537,160	$ 8,182,119
Ultramax Vessels
Property, Plant and Equipment [Line Items]
Number of vessels acquired | vessel					6		6
Vessel purchase price					$ 122,800,000		$ 122,800,000
Number of vessels delivered | vessel					3		3
Proceeds from issuance of notes					$ 62,100,000		$ 62,100,000
Deposits on vessel purchases					6,000,000
Kestrel Vessel
Property, Plant and Equipment [Line Items]
Proceeds from sale of vessels	$ 7,000,000
Gain on sale of vessels					1,000,000		1,000,000
Vessel Thrasher
Property, Plant and Equipment [Line Items]
Proceeds from sale of vessels		$ 9,800,000
Gain on sale of vessels							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				$ 6,700,000
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					$ 52,000,000		52,000,000
Scrubbers and BWTS reclassified							4,300,000
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
Scrubbers and BWTS reclassified							1,600,000
Amount recorded in balance sheet							$ 3,400,000