Long-Term Debt (Covenants) (Details) $ in Millions	Jun. 08, 2017 USD ($) item	Nov. 07, 2017 item	May 31, 2017 USD ($) item	Mar. 31, 2015 USD ($)
2015 Debt Facility
Long-Term Debt
Number of debt principal payments with relaxed covenants | item			2
Minimum cash balance requirement through six months from the Amendment Date			$ 18.0
Minimum cash per mortgaged vessel through six months from the Amendment Date			1.0
Minimum cash balance requirement from six months from the amendment date through first anniversary			29.0
Minimum cash per mortgaged vessel from six months from the Amendment Date through first anniversary			1.6
Minimum cash balance requirement from first anniversary through thereafter			40.0
Minimum cash per mortgaged vessel from first anniversary through thereafter			2.2
Minimum stock offering for recalculation of restricted cash covenants			$ 50.0
Percent of principal debt outstanding for recalculation of restricted cash covenants (as a percent)			5.00%
Minimum cash balance required to be maintained if common stock offering met required threshold			$ 20.0
Minimum cash per mortgaged vessel if common stock offering met threshold			$ 1.1
Minimum interest coverage ratio for following 12 month period (as a percent)			125.00%
Minimum interest coverage ratio for following subsequent year (as a percent)			150.00%
Minimum interest coverage ratio for thereafter (as a percent)			250.00%
Minimum fair market value of mortgaged ships plus any additional security over the outstanding loan balance through March 31, 2018			125.00%
Minimum fair market value of mortgaged ships plus any additional security over the outstanding loan balance from April 1, 2018 through March 31, 2019			130.00%
Minimum fair market value of mortgaged ships plus any additional security over the outstanding loan balance thereafter			135.00%
Amendment fees			$ 1.1
Original loan amount				$ 758.0
The amount of restricted cash released			$ 26.8
2017 Bridge Loan
Long-Term Debt
Minimum interest coverage ratio for following 12 month period (as a percent)	125.00%
Minimum interest coverage ratio for following subsequent year (as a percent)	150.00%
Original loan amount	$ 97.0
The amount of restricted cash released	$ 6.0
Number of VLGC secured by loan agreement | item	4	4
Minimum consolidated liquidity	$ 50.0
Minimum cash and cash equivalents, including restricted cash freely available and unencumbered basis	$ 10.0
Maximum consolidated net debt to consolidated total capitalization ratio (as a percent)	60.00%
Minimum stockholder's equity balance	$ 400.0
Percent of any new equity raised after closing date (as a percent)	50.00%
Percent of positive net income for the immediately preceding financial year (as a percent)	25.00%
Current assets and long-term restricted cash divided by current liabilities ratio (as a percent)	100.00%
Minimum aggregate market value to principal amount outstanding ratio (as a percent)	150.00%
2017 Bridge Loan | LIBOR | Period Ending December 7, 2017
Long-Term Debt
Margin added to LIBOR for interest rate on loan facility (as a percent)	2.50%
2017 Bridge Loan | LIBOR | December 8, 2017 until March 7, 2018
Long-Term Debt
Margin added to LIBOR for interest rate on loan facility (as a percent)	4.50%
2017 Bridge Loan | LIBOR | March 8, 2018 until June 7, 2018
Long-Term Debt
Margin added to LIBOR for interest rate on loan facility (as a percent)	6.50%
2017 Bridge Loan | LIBOR | June 8, 2018 until Maturity Date
Long-Term Debt
Margin added to LIBOR for interest rate on loan facility (as a percent)	8.50%
Royal Bank of Scotland plc (RBS)
Long-Term Debt
Debt redemption price (as a percent)	96.00%