Vessels and vessel improvements - Narrative (Details)			3 Months Ended		12 Months Ended
	Aug. 30, 2017 USD ($)	Feb. 28, 2017 USD ($) vessel	Dec. 31, 2016 USD ($) vessel group t	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) vessel t	Dec. 31, 2016 USD ($) vessel group t	Dec. 31, 2015 USD ($) vessel	Dec. 19, 2017 USD ($)	Nov. 14, 2016 USD ($) t
Property, Plant and Equipment [Line Items]
Number of vessels | vessel			16		47	16
Number of vessels expected to be sold | vessel							6
Impairment of assets to be sold			$ 122,860,600	$ 6,167,262			$ 50,872,734
Carrying value of assets to be sold			$ 234,860,600			$ 234,860,600	76,332,734
Number of groups of vessels | group			2			2
Number of vessels in group one | vessel			5			5
Dead weight tonnage of fleet to be divested | t			53,000			53,000
Number of vessels in group two | vessel			11			11
Age of vessel						13 years
Period of time vessels are to be sold						2 years
Number of vessels sold | vessel					2
Carrying capacity (in dead weight tonnage) | t					2,683,751
Proceeds from sale of vessels					$ 26,042,000	$ 13,001,000	4,235,542
Gain on sale of vessel					$ 2,134,767	$ (101,860)	$ (5,696,675)
SDARI-64 Ultramax Dry Bulk Vessel
Property, Plant and Equipment [Line Items]
Carrying capacity (in dead weight tonnage) | t									64,000
Vessel purchase price									$ 17,900,000
Vessels Redwing, Sparrow, Woodstar and Wren
Property, Plant and Equipment [Line Items]
Number of vessels sold | vessel					4
Proceeds from sale of vessels					$ 26,000,000
Gain on sale of vessel					2,100,000
Vessel Avocet
Property, Plant and Equipment [Line Items]
Proceeds from sale of vessels	$ 9,600,000
Gain on sale of vessel	$ 300,000
2015 Built Ultramax Vessel
Property, Plant and Equipment [Line Items]
Vessel purchase price								$ 21,275,000
Deposit paid on purchase of vessel					$ 2,200,000
Eagle Bulk Ultraco LLC | Greenship Vessels
Property, Plant and Equipment [Line Items]
Number of vessels to be purchased | vessel		9
Number of vessels delivered | vessel		9			9
Vessel agreement, aggregate purchase price		$ 153,000,000
Vessel agreement, purchase price per vessel		$ 17,000,000