Vessels, Net (Details)	6 Months Ended
	Sep. 30, 2018 USD ($) item	Mar. 31, 2018 USD ($)
Accumulated depreciation
Vessels, net	$ 1,507,941,555	$ 1,539,111,833
The number of vessels with contracts to purchase exhaust gas cleaning systems | item	7
Vessels
Cost
Balance at the beginning of the period	$ 1,728,987,980
Other additions	1,213,621
Balance at the end of the period	1,730,201,601
Accumulated depreciation
Balance at the beginning of the period	(189,876,147)
Impairment	0
Depreciation	(32,383,899)
Balance at the end of the period	$ (222,260,046)
Number of vessels with capital improvements | item	8
The number of vessels with contracts to purchase exhaust gas cleaning systems | item	4
Mortgaged VLGC vessels, carrying value	$ 1,507,900,000	$ 1,539,100,000