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Debt and Financing Obligation - Additional Information (Details)									1 Months Ended		3 Months Ended		12 Months Ended
	Jan. 31, 2019 USD ($)	Jan. 09, 2019 USD ($)	Dec. 31, 2018	Dec. 21, 2018 USD ($) Project MW	Dec. 13, 2018 USD ($) MW	Sep. 30, 2018	Jun. 30, 2018	Mar. 28, 2018 USD ($)	Jan. 31, 2019 USD ($) Position Employee	Nov. 30, 2015 USD ($) Position	Jan. 31, 2019 USD ($)	Jan. 31, 2018 USD ($)	Oct. 31, 2017	Oct. 31, 2016 USD ($)	Apr. 01, 2020 USD ($)	Apr. 01, 2019	Oct. 31, 2018 USD ($)	Oct. 01, 2018 USD ($)	Nov. 30, 2016 USD ($)	Apr. 30, 2016 USD ($)	Mar. 05, 2013 USD ($)
Debt Instrument [Line Items]
Proceeds from Issuance of Debt											$ 17,250,000	$ 0
Lease payment term	36 months								36 months		36 months
Minimum [Member]
Debt Instrument [Line Items]
Optional project financing term											5 years
Connecticut Green Bank Note [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity																					$ 5,900,000
Debt Instrument, Interest Rate, Stated Percentage																					5.00%
Long-term Line of Credit	$ 6,052,000								$ 6,052,000		$ 6,052,000						$ 6,052,000
PNC Energy Capital, LLC [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	45,700,000								45,700,000		$ 45,700,000						46,100,000
Term of loan											10 years
State of Connecticut [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	10,000,000								$ 10,000,000	$ 10,000,000	$ 10,000,000						10,000,000
Loan forgiveness terms											if the Company created 165 full-time positions and retained 538 full-time positions for two consecutive years (the “Employment Obligation”) as measured on October 28, 2017 (the “Target Date”). The Agreement was subsequently amended in April 2017 to extend the Target Date by two years to October 28, 2019
State of Connecticut [Member] \| Employment Obligation [Member]
Debt Instrument [Line Items]
Number of full time positions required to be created \| Position										165
Number of full time positions required to be retained \| Position										538
State of Connecticut [Member] \| Employment Obligation [Member] \| Second Amendment [Member]
Debt Instrument [Line Items]
Number of full time positions required to be maintained \| Employee									538
Number of consecutive months maintain the full time positions									24 months
Additional number of full time positions required to be create \| Position									91
Additional credits to be earned	$ 2,000,000								$ 2,000,000		$ 2,000,000
State of Connecticut [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Percentage of loan forgiveness	50.00%
Hercules Capital, Inc. [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 25,000,000								25,000,000		25,000,000									$ 25,000,000
Long-term Line of Credit	$ 25,488,000							$ 11,900,000	$ 25,488,000		$ 25,488,000						25,343,000
Proceeds from Issuance of Debt														$ 20,000,000
Term of loan											30 months
Debt Instrument, Interest Rate, Stated Percentage Rate Range			10.90%			10.65%	10.40%	10.15%			9.90%
Other Deductions and Charges																	1,700,000	$ 1,700,000
Loan Advance								$ 13,100,000
Term Loan Maturity Date											Apr. 01, 2020
Debt instrument, basis spread on variable rate											4.50%
Hercules Capital, Inc. [Member] \| Series C Preferred Stock [Member]
Debt Instrument [Line Items]
Debt instrument, amendment description											As collateral for obligations under the Hercules Agreement, the Company granted Hercules a security interest in FuelCell Energy, Inc.’s existing and thereafter-acquired assets except for intellectual property and certain other excluded assets. The collateral does not include assets held by FuelCell Energy Finance, LLC (“FuelCell Finance”) or any project subsidiary thereof. The Company may continue to collateralize and finance its project subsidiaries through other lenders and partners. As of January 31, 2019, the Hercules Agreement, as amended, included a minimum cash covenant requiring the Company to maintain an unrestricted cash balance in accounts subject to an account control agreement in favor of Hercules of at least the greater of (a) 75% of the outstanding loan balance plus (b) the amount of accounts payable (as defined under GAAP) not paid within 90 days of the invoice date. (See Note 17, “Subsequent Events” for a discussion of a further amendment to the Hercules Agreement and the minimum cash covenant.) The Hercules Agreement, as amended, contains customary representations and warranties, affirmative and negative covenants, and events of default that entitle Hercules to cause the indebtedness under the agreement to become immediately due and payable.
Cash covenant minimum required percentage of unrestricted cash balance on outstanding loan balance and accounts payable	75.00%								75.00%		75.00%
Hercules Capital, Inc. [Member] \| Scenario Forecast [Member]
Debt Instrument [Line Items]
Other Deductions and Charges															$ 900,000
Cash covenant minimum required percentage of unrestricted cash balance on outstanding loan balance and accounts payable																75.00%
Hercules Capital, Inc. [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range												10.00%
Hercules Capital, Inc. [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range													9.75%
Webster Bank Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range											5.00%
Notes Payable to Bank, Current	$ 1,000,000								$ 1,000,000		$ 1,000,000						$ 1,100,000		$ 2,300,000
NRG Energy [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	40,000,000								40,000,000		40,000,000
Long-term Line of Credit	5,750,000				$ 0				5,750,000		$ 5,750,000
NRG Energy [Member] \| Tulare BioMAT [Member] \| California [Member]
Debt Instrument [Line Items]
Capacity of Plant \| MW					2.8
NRG Energy [Member] \| Central CA Fuel Cell 2, LLC [Member]
Debt Instrument [Line Items]
Loan Advance					$ 5,800,000
NRG Energy [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range											8.50%
NRG Energy [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range											8.00%
Generate Lending Construction Loan Agreement [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	10,000,000								10,000,000		$ 10,000,000
Generate Lending Construction Loan Agreement [Member] \| FuelCell Energy Finance II, LLC [Member] \| Generate Lending, LLC [Member]
Debt Instrument [Line Items]
Loan Advance				$ 10,000,000
Debt instrument, basis spread on variable rate				9.50%
Percentage of construction budget				100.00%
Unlevered internal rate of return percentage to lender				10.00%
Availability period for working capital loans				36 months
Equity ownership				100.00%
Purchase price adjustment				50.00%
Draw down fee percentage				3.00%
Disposition fee percentage of total sale price				3.00%
Generate Lending Construction Loan Agreement [Member] \| FuelCell Energy Finance II, LLC [Member] \| Generate Lending, LLC [Member] \| PSEG Long Island [Member]
Debt Instrument [Line Items]
Capacity of Plant \| MW				39.8
Number of projects expected to be completed \| Project				3
Generate Lending Construction Loan Agreement [Member] \| FuelCell Energy Finance II, LLC [Member] \| Generate Lending, LLC [Member] \| DEEP RFP [Member]
Debt Instrument [Line Items]
Capacity of Plant \| MW				22.2
Number of projects expected to be completed \| Project				2
Generate Lending Construction Loan Agreement [Member] \| California [Member] \| FuelCell Energy Finance II, LLC [Member] \| Generate Lending, LLC [Member] \| Bolthouse Farms [Member]
Debt Instrument [Line Items]
Capacity of Plant \| MW				5
Generate Lending Construction Loan Agreement [Member] \| Maximum [Member] \| FuelCell Energy Finance II, LLC [Member] \| Generate Lending, LLC [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 300,000,000
Line of credit facility, current borrowing capacity				$ 100,000,000
Generate Lending Construction Loan Agreement [Member] \| Minimum [Member] \| FuelCell Energy Finance II, LLC [Member] \| Generate Lending, LLC [Member]
Debt Instrument [Line Items]
Unlevered internal rate of return percentage to lender				10.00%
After-tax yield percentage				12.00%
Tranche One [Member]
Debt Instrument [Line Items]
Aggregate working capital loan amount minimum limit				$ 100,000,000
Aggregate working capital loan amount maximum limit				$ 200,000,000
Disposition fee percentage				2.00%
Tranche Two [Member]
Debt Instrument [Line Items]
Aggregate working capital loan amount minimum limit				$ 200,000,000
Aggregate working capital loan amount maximum limit				$ 300,000,000
Disposition fee percentage				1.00%
Enhanced Capital Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 1,500,000
Long-term Line of Credit	$ 1,500,000								$ 1,500,000		$ 1,500,000
Debt instrument, basis spread on variable rate		6.00%
Debt instrument, maturity period description		The loan maturity date is three years from the date of the Enhanced Capital Loan Agreement upon which the outstanding principal and accrued interest will be payable.
Debt instrument, maturity period		3 years