Commitments and Contingencies (Details) $ in Millions			1 Months Ended	3 Months Ended
	May 04, 2018 t $ / d	May 10, 2017 USD ($) t $ / d	Oct. 31, 2014 t $ / d	Mar. 31, 2018 t
Property, Plant and Equipment [Line Items]
Dead weight tonnage of operating fleet | t				2,746,891
Japanese Vessel
Property, Plant and Equipment [Line Items]
Dead weight tonnage of operating fleet | t			37,000
Charters agreement term			7 years
Charters agreement term, extension option			1 year
Vessel agreement, termination fee | $		$ 1.5
Japanese Vessel | First Seven Years
Property, Plant and Equipment [Line Items]
Vessel hiring rate (in dollars per day)			13,500
Japanese Vessel | Eighth Year Option
Property, Plant and Equipment [Line Items]
Vessel hiring rate (in dollars per day)			13,750
2013 Built Japanese Vessel
Property, Plant and Equipment [Line Items]
Dead weight tonnage of operating fleet | t		61,400		61,400
Charters agreement term		3 years		3 years
Charters agreement term, extension option		2 years
2013 Built Japanese Vessel | First Four Years
Property, Plant and Equipment [Line Items]
Vessel hiring rate (in dollars per day)		12,800
2013 Built Japanese Vessel | First Optional Year
Property, Plant and Equipment [Line Items]
Vessel hiring rate (in dollars per day)		13,800
2013 Built Japanese Vessel | Second Optional Year
Property, Plant and Equipment [Line Items]
Vessel hiring rate (in dollars per day)		14,300
Subsequent Event | Ultramax Vessels
Property, Plant and Equipment [Line Items]
Dead weight tonnage of operating fleet | t	61,425
Charters agreement term	3 years
Charters agreement term, extension option	2 years
Vessel hiring rate (in dollars per day)	12,700
Subsequent Event | Ultramax Vessels | First Optional Year
Property, Plant and Equipment [Line Items]
Vessel hiring rate (in dollars per day)	13,750
Subsequent Event | Ultramax Vessels | Second Optional Year
Property, Plant and Equipment [Line Items]
Vessel hiring rate (in dollars per day)	14,750