Subsequent Events - Additional Information (Details)								3 Months Ended				6 Months Ended
	Jun. 26, 2019 USD ($)	Jun. 17, 2019 USD ($) shares	Jun. 11, 2019 USD ($)	Jun. 10, 2019 $ / shares shares	May 15, 2019 USD ($)	May 09, 2019 USD ($) MW	May 08, 2019 USD ($)	Apr. 30, 2019 USD ($) shares	Jan. 31, 2019 USD ($)	Apr. 30, 2018 USD ($)	Jan. 31, 2018 USD ($)	Apr. 30, 2019 USD ($) TradingDay shares	Apr. 30, 2018 USD ($)	Jun. 13, 2019 USD ($) shares	May 01, 2019	Apr. 01, 2019	Mar. 29, 2019	Feb. 28, 2019	Oct. 31, 2018 USD ($) shares	Aug. 29, 2018 shares
Subsequent Event [Line Items]
Divend declared								$ 800,000	$ 800,000	$ 800,000	$ 800,000
Convertible preferred stock, reduction in carrying amount								10,400,000				$ 12,300,000
Series B Cumulative Convertible Perpetual Preferred Stock [Member]
Subsequent Event [Line Items]
Divend declared								800,000		$ 800,000		$ 1,600,000	$ 1,600,000
Preferred stock, dividend rate, percentage												5.00%	5.00%
Temporary equity, carrying amount, attributable to parent								$ 59,857,000				$ 59,857,000							$ 59,857,000
Preferred stock sale of shares | shares								64,020				64,020							64,020
Preferred stock shares outstanding | shares								64,020				64,020							64,020
Series C Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock, dividend rate, percentage												15.00%
Convertible preferred stock, converted into common stock | shares								5,852				7,374
Temporary equity, carrying amount, attributable to parent								$ 3,162,000				$ 3,162,000							$ 7,480,000
Redemption pice percentage												125.00%
Series D Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock, dividend rate, percentage												15.00%
Convertible preferred stock, converted into common stock | shares								6,964				12,218
Temporary equity, carrying amount, attributable to parent								$ 20,546,000				$ 20,546,000							$ 27,392,000
Reduced conversion price | $ / shares				$ 0.4619
Percentage of lowest volume weighted average price of common stock considered as conversion price												85.00%
Number of consecutive trading days | TradingDay												5
Preferred stock sale of shares | shares								18,462				18,462		8,396					30,680	30,680
Preferred stock shares outstanding | shares								18,462				18,462		8,396					30,680
Preferred stock liquidation value														$ 8,400,000
Redemption pice percentage												125.00%
Common Stock [Member]
Subsequent Event [Line Items]
Shares issued due to conversion of series D preferred shares | shares				12,100,000
Hercules Capital, Inc. [Member]
Subsequent Event [Line Items]
Credit agreement, maturity date												Apr. 01, 2020
Debt instrument, basis spread on variable rate												4.50%
Cash covenant minimum required percentage of unrestricted cash balance on outstanding loan balance and accounts payable															75.00%	75.00%	50.00%	50.00%
Hercules Capital, Inc. [Member] | Scenario Forecast [Member] | EMRE [Member]
Subsequent Event [Line Items]
Repayment of loan	$ 6,000,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Default interest rate per annum			5.00%
Prepayment charge payment waive percentage on outstanding loan			2.00%
Convertible preferred stock, converted into number of common stock shares | shares		1,658,861
Subsequent Event [Member] | Series B Cumulative Convertible Perpetual Preferred Stock [Member]
Subsequent Event [Line Items]
Divend declared					$ 0
Dividends payment date					May 15, 2019
Aggregate amount of dividend payment					$ 800,000
Preferred stock, dividend rate, percentage					25.00%
Dividends payable					$ 1,000,000
Subsequent Event [Member] | Series C Preferred Stock [Member]
Subsequent Event [Line Items]
Convertible preferred stock, converted into common stock | shares		1,618
Convertible preferred stock, reduction in carrying amount		$ 3,200,000
Temporary equity, carrying amount, attributable to parent		$ 0
Subsequent Event [Member] | EMRE [Member]
Subsequent Event [Line Items]
License agreement payment	$ 4,000,000		$ 10,000,000
Subsequent Event [Member] | Hercules Capital, Inc. [Member]
Subsequent Event [Line Items]
Non-refundable fee paid							$ 250,000
Repayment of loan			1,400,000
Outstanding principal balance			$ 20,900,000
Subsequent Event [Member] | Hercules Capital, Inc. [Member] | Commencing on May 1, 2019 through 2:00 pm Eastern Time on June 7, 2019 [Member]
Subsequent Event [Line Items]
Cash covenant minimum required percentage of unrestricted cash balance on outstanding loan balance and accounts payable							40.00%
Subsequent Event [Member] | Hercules Capital, Inc. [Member] | After 2:00 pm Eastern Time on June 7, 2019 [Member]
Subsequent Event [Line Items]
Cash covenant minimum required percentage of unrestricted cash balance on outstanding loan balance and accounts payable							75.00%
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member]
Subsequent Event [Line Items]
Business acquisition, purchase price						$ 35,500,000
Working capital post-closing adjustment for purchase price						1,000,000
Restricted cash on hand						$ 15,000,000
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Credit Agreement [Member]
Subsequent Event [Line Items]
Credit agreement, maturity date						May 09, 2025
Interest rate description						The interest rate under the Credit Agreement fluctuates monthly at the 30-day LIBOR rate plus 275 basis points
Debt instrument, interest rate basis term						30 days
Debt instrument, basis spread on variable rate						2.75%
Debt instrument, total notional value						$ 25,000,000
Debt instrument, covenant terms						The Credit Agreement also requires BFC to maintain a debt service reserve at each of Liberty Bank and Fifth Third of $1.25 million, which debt service reserves were funded on May 10, 2019, to be held in deposit accounts at each respective bank, with funds to be disbursed with the consent of or at the request of the required lenders in their sole discretion. Each of Liberty Bank and Fifth Third also has an operation and module replacement reserve (“O&M Reserve”) of $250.0 thousand, both of which were funded at closing, to be held in deposit accounts at each respective bank, and thereafter BFC is required to deposit $100.0 thousand per month into each O&M Reserve for the first five years of the Credit Agreement, with such funds to be released at the sole discretion of Liberty Bank and Fifth Third, as applicable. BFC is also required to maintain excess cash flow reserve accounts at each of Liberty Bank and Fifth Third and to deposit 50% of the excess cash flows from the Bridgeport Fuel Cell Project into these accounts. Excess cash flow consists of cash generated by BFC from the Bridgeport Fuel Cell Project after payment of all expenses (including after payment of service fees to the Company), debt service to Liberty Bank and Fifth Third, the funding of all required reserves, and payments to Connecticut Green Bank for the subordinated facility (as described below). BFC is also required to maintain a debt service coverage ratio of not less than 1.20, measured annually. The Credit Agreement contains customary representations, warranties and covenants.
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Credit Agreement [Member] | Minimum [Member]
Subsequent Event [Line Items]
Debt service coverage ratio						120.00%
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Credit Agreement [Member] | Interest Rate Swap [Member]
Subsequent Event [Line Items]
Derivative, fixed rate of interest						2.34%
Derivative, floating index rate						2.75%
Net interest rate						5.09%
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Credit Agreement [Member] | Fifth Third Bank [Member]
Subsequent Event [Line Items]
Proceeds from long-term lines of credit						$ 12,500,000
Debt service reserves required to be maintained and held in deposit accounts						1,250,000
Operation and module replacement reserves required to be maintained and held in deposit accounts						250,000
Operation and module replacement reserve to be deposited per month						$ 100,000
Percentage of excess cash flows to be maintained in accounts						50.00%
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Credit Agreement [Member] | Liberty Bank [Member]
Subsequent Event [Line Items]
Proceeds from long-term lines of credit						$ 12,500,000
Debt service reserves required to be maintained and held in deposit accounts						1,250,000
Operation and module replacement reserves required to be maintained and held in deposit accounts						250,000
Operation and module replacement reserve to be deposited per month						$ 100,000
Percentage of excess cash flows to be maintained in accounts						50.00%
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Subordinated Credit Agreement [Member]
Subsequent Event [Line Items]
Proceeds from long-term lines of credit						$ 6,000,000
Debt instrument, covenant terms						In addition, on May 9, 2019, in connection with the closing of the purchase of BFC, BFC entered into a subordinated credit agreement with the Connecticut Green Bank whereby Connecticut Green Bank provided financing in the amount of $6.0 million (the “Subordinated Credit Agreement”), $1.8 million of which was used to collateralize a letter of credit issued by Liberty Bank to satisfy a performance assurance requirement in the Energy Purchase Agreement with Connecticut Light and Power Company and the balance of which was applied toward outstanding principal on the Company’s existing indebtedness to Connecticut Green Bank. As security for the Subordinated Credit Agreement, Connecticut Green Bank received a perfected lien, subordinated and second in priority to the liens securing the $25.0 million (senior term loan amount) loaned under the Credit Agreement, in all of the same collateral securing the Credit Agreement. The interest rate under the Subordinated Credit Agreement is 8% per annum. A commitment fee of $60.0 thousand was earned by Connecticut Green Bank in connection with the closing. The debt service coverage ratio required to be maintained under the Subordinated Credit Agreement may not be less than 1.10 as of the end of each fiscal quarter. The term of the Subordinated Credit Agreement expires 7 years from the date of the advance of the loan. Principal and interest are due monthly in amounts sufficient to fully amortize the loan over an 84 month period. However, monthly debt service payments can accumulate in arrearages in the event that BFC does not have sufficient cash to make any monthly debt service payment. BFC has the right to make additional principal payments or pay the balance in full at any time without additional fees or penalties. The Subordinated Credit Agreement also contains customary representations, warranties and covenants.
Debt instrument, interest rate						8.00%
Line of credit, commitment fee						$ 60,000
DebtInstrument term						7 years
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Subordinated Credit Agreement [Member] | Letter of Credit [Member]
Subsequent Event [Line Items]
Line of credit collateral						$1.8
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Subordinated Credit Agreement [Member] | Senior Term Loan [Member]
Subsequent Event [Line Items]
Liens securing senior term loan amount						$ 25,000,000
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Subordinated Credit Agreement [Member] | Minimum [Member]
Subsequent Event [Line Items]
Debt service coverage ratio						110.00%
Subsequent Event [Member] | Bridgeport Fuel Cell, LLC [Member] | Bridgeport, Connecticut [Member]
Subsequent Event [Line Items]
Capacity of Plant | MW						14.9
Plant operation period						5 years