Debt - Additional Information (Details)						1 Months Ended				3 Months Ended	12 Months Ended
	Apr. 24, 2020 USD ($)	Nov. 22, 2019 USD ($) $ / shares MW shares	May 09, 2019 USD ($) MW	Feb. 28, 2019 USD ($) MW	Jan. 09, 2019 USD ($)	Jun. 08, 2020 USD ($)	Apr. 30, 2019 USD ($)	Jan. 31, 2019 USD ($) Position	Oct. 31, 2015 USD ($) Position	Oct. 31, 2020 USD ($) $ / shares	Oct. 31, 2020 USD ($) $ / shares	Oct. 31, 2019 USD ($) $ / shares shares	Oct. 31, 2018 USD ($)	Oct. 06, 2020 $ / shares	Apr. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	May 16, 2019	Feb. 06, 2019 USD ($)
Debt Instrument [Line Items]
Long-term line of credit, discount										$ 5,152,000	$ 5,152,000	$ 4,251,000
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares										$ 0.242	$ 0.242			$ 0.242
Class of warrants or rights issued value												3,900,000
Interest expense											$ 15,294,000	$ 10,623,000	$ 9,055,000
Sale-leaseback Arrangements with PNC [Member]
Debt Instrument [Line Items]
Purchase right percentage of projected assets at fair market value											31.00%
Liberty Bank [Member] | CARES Act [Member]
Debt Instrument [Line Items]
Net proceeds from PPP Note											$ 2,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member]
Debt Instrument [Line Items]
Percentage of aggregate principal amount on discount												2.50%
Percentage of cash interest paid											9.90%
Percentage of payment-in-kind interest											2.05%
Class of warrants or rights issued value												$ 3,900,000
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Senior Secured Credit Facility [Member]
Debt Instrument [Line Items]
Long-term line of credit												200,000,000.0
Long-term Line of Credit												200,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Initial Funding [Member]
Debt Instrument [Line Items]
Drew down to fully repay debt outstanding												14,500,000
Long-term line of credit after discount												14,100,000
Long-term line of credit, discount												$ 400,000
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares												$ 0.310
Debt instrument term											7 years
Quarterly payment payable date											Oct. 31, 2027
Administrative fee											$ 100,000
Debt instrument, description											Outstanding principal under the Orion Facility was to be amortized on a straight-line basis over a seven-year term with the initial payment due 21 business days after the end of the first quarter of fiscal year 2021. The maturity date of the Orion Facility was October 31, 2027.  The Orion Facility contained an administrative fee of $0.1 million per year paid on a quarterly basis and also included a prepayment premium of up to 35%.  Such prepayment fee was to be reduced over time based on the aggregate amount of principal and interest paid.
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Initial Funding [Member] | Maximum [Member]
Debt Instrument [Line Items]
Number Of Securities Called By Warrants | shares												6,000,000
Percentage of premium prepaid amount											35.00%
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member]
Debt Instrument [Line Items]
Drew down to fully repay debt outstanding		$ 65,500,000
Long-term line of credit after discount		63,900,000
Long-term line of credit, discount		$ 1,600,000
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member] | Exercise Price 0.242 [Member]
Debt Instrument [Line Items]
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares		$ 0.242
Class of warrants or rights exercised | shares		8,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member] | Exercise Price 0.620 [Member]
Debt Instrument [Line Items]
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares		$ 0.620
Class of warrants or rights exercised | shares		6,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member] | Groton Project [Member]
Debt Instrument [Line Items]
Capacity of plant | MW		7.4
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member] | LIPA Yaphank Solid Waste Management Project [Member]
Debt Instrument [Line Items]
Capacity of plant | MW		7.4
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member] | Tulare BioMAT [Member]
Debt Instrument [Line Items]
Capacity of plant | MW		2.8
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member] | Maximum [Member]
Debt Instrument [Line Items]
Class of warrants or rights issued | shares		14,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member]
Debt Instrument [Line Items]
Credit agreement requires to establish debt reserve										$ 5,000,000.0	$ 5,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Secondary Facility Loans[Member]
Debt Instrument [Line Items]
Credit agreement to establish additional covenants expired unused										35,000,000	35,000,000
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Fifth Orion Amendment [Member]
Debt Instrument [Line Items]
Agreed to pay option premium in exchange for loan commitment						$ 1,000,000.0
Interest expense										1,000,000.0
Connecticut Green Bank Loan [Member]
Debt Instrument [Line Items]
Long-term line of credit										$ 4,800,000	$ 4,800,000
Line of credit facility, maximum borrowing capacity												$ 1,800,000				$ 3,000,000.0
Debt instrument, interest rate, stated percentage rate										8.00%	8.00%
Long-term Line of Credit										$ 4,800,000	$ 4,800,000
Connecticut Green Bank Loan [Member] | Groton Commitment Letter [Member]
Debt Instrument [Line Items]
Subordinated project term loan																		$ 5,000,000.0
Subordinated Credit Agreement [Member] | Bridgeport Fuel Cell, LLC [Member] | Connecticut Green Bank Loans [Member]
Debt Instrument [Line Items]
Long-term line of credit										5,100,000	5,100,000
Capacity of plant | MW			14.9
Debt instrument, interest rate, stated percentage rate			8.00%
Long-term Line of Credit										5,100,000	$ 5,100,000
Proceeds from long-term lines of credit			$ 6,000,000.0
Debt instrument, covenant terms											On May 9, 2019, in connection with the closing of the purchase of the membership interests of Bridgeport Fuel Cell, LLC (“BFC”) (and the 14.9 MW Bridgeport Fuel Cell Project), 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”). This $6.0 million consisted of $1.8 million in incremental funding that was received by BFC and $4.2 million of funding previously received by FuelCell Energy, Inc. with respect to which BFC became the primary obligor. 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 loaned under the BFC Credit Agreement (as defined below), in all of the same collateral securing the BFC Credit Agreement. The interest rate under the Subordinated Credit Agreement is 8% per annum. Principal and interest are due monthly in amounts sufficient to fully amortize the loan over an 84-month period ending in May 2026. The Subordinated Credit Agreement contains a debt coverage ratio which is required to be maintained and may not be less than 1.10 as of the end of each fiscal quarter, beginning with the quarter ended July 31, 2020. The balance under the Subordinated Credit Agreement as of October 31, 2020 was $5.1 million
Subordinated Credit Agreement [Member] | Minimum [Member] | Bridgeport Fuel Cell, LLC [Member] | Connecticut Green Bank Loans [Member]
Debt Instrument [Line Items]
Debt service coverage ratio			110.00%
Subordinated Credit Agreement [Member] | Incremental Funding | Bridgeport Fuel Cell, LLC [Member] | Connecticut Green Bank Loans [Member]
Debt Instrument [Line Items]
Proceeds from long-term lines of credit			$ 1,800,000
Subordinated Credit Agreement [Member] | Incremental Funding [Member] | Bridgeport Fuel Cell, LLC [Member] | Connecticut Green Bank Loans [Member]
Debt Instrument [Line Items]
Proceeds from long-term lines of credit			4,200,000
Subordinated Credit Agreement [Member] | Senior Term Loan [Member] | Bridgeport Fuel Cell, LLC [Member] | Connecticut Green Bank Loans [Member]
Debt Instrument [Line Items]
Liens securing senior term loan amount			$ 25,000,000.0
Credit Agreement | Bridgeport Loans [Member]
Debt Instrument [Line Items]
Debt instrument, covenant terms											The BFC Credit Agreement requires BFC to maintain a debt service reserve. Each of Liberty Bank and Fifth Third Bank also has an operation and module replacement reserve (“O&M Reserve”) under the BFC Credit Agreement. BFC is required to deposit $100,000 per month into each O&M Reserve for the first five years of the BFC Credit Agreement, with such funds to be released at the sole discretion of Liberty Bank and Fifth Third Bank, as applicable. BFC is also required to maintain excess cash flow reserve accounts at each of Liberty Bank and Fifth Third Bank. Excess cash flow consists of cash generated by BFC from the Bridgeport Fuel Cell Project after payment of all expenses (including after payment of intercompany service fees to the Company), debt service to Liberty Bank and Fifth Third Bank, the funding of all required reserves, and payments to Connecticut Green Bank for the subordinated facility.  BFC is also required to maintain a debt service coverage ratio of not less than 1.20, measured for the trailing year based on fiscal quarters beginning with the quarter ended July 31, 2020. The Company has certain quarterly and annual financial reporting requirements under the BFC Credit Agreement. The annual financial statements to be provided pursuant to such requirements are to be audited and accompanied by a report of an independent certified public accountant, which report shall not include a “going concern” matter of emphasis or any qualification as to the scope of such audit.
Maturity date			May 09, 2025
Interest rate description											The interest rate under the BFC Credit Agreement fluctuates monthly at the 30-day LIBOR rate plus 275 basis points
Debt instrument, interest rate basis term			30 days
Credit Agreement | Bridgeport Loans [Member] | Interest Rate Swap
Debt Instrument [Line Items]
Net interest rate																	5.09%
Credit Agreement | Bridgeport Loans [Member] | Fair Value, Inputs, Level 2 | Interest Rate Swap
Debt Instrument [Line Items]
Fair value adjustments, charge											$ 300,000	600,000
Fair value interest rate										900,000	900,000	600,000
Credit Agreement | Bridgeport Loans [Member] | Fifth Third Bank [Member]
Debt Instrument [Line Items]
Operation and module replacement reserve to be deposited per month										100,000	100,000
Credit Agreement | Bridgeport Loans [Member] | Liberty Bank [Member]
Debt Instrument [Line Items]
Operation and module replacement reserve to be deposited per month										100,000	$ 100,000
Credit Agreement | Bridgeport Fuel Cell, LLC [Member] | Bridgeport Loans [Member] | Fifth Third Bank [Member]
Debt Instrument [Line Items]
Proceeds from long-term lines of credit			$ 12,500,000
Credit Agreement | Bridgeport Fuel Cell, LLC [Member] | Bridgeport Loans [Member] | Liberty Bank [Member]
Debt Instrument [Line Items]
Proceeds from long-term lines of credit			$ 12,500,000
Credit Agreement | Minimum [Member] | Bridgeport Loans [Member]
Debt Instrument [Line Items]
Debt service coverage ratio											120.00%
Finance Obligations for Sale Leaseback Agreements [Member] | PNC Energy Capital, LLC [Member]
Debt Instrument [Line Items]
Long-term line of credit										49,300,000	$ 49,300,000	45,200,000
Long-term Line of Credit										49,300,000	49,300,000	45,200,000
Embedded gain on termination of lease											29,000,000.0
State of Connecticut [Member]
Debt Instrument [Line Items]
Debt instrument term									15 years
Debt instrument, interest rate, stated percentage rate									2.00%
Debt Instrument, Face Amount									$ 10,000,000.0	9,454,000	$ 9,454,000	10,000,000			$ 10,000,000.0
Debt instrument, payment terms, period principal payments are deferred									4 years
Debt instrument, date of first required payment									Dec. 01, 2019
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 Assistance Agreement was subsequently amended in April 2017 to extend the Target Date by two years to October 28, 2019.
Debt instrument period for deferment of principal and interest payments											3 months
Debt instrument, payment terms											In April of 2020, as a result of the COVID-19 pandemic, the State of Connecticut agreed to defer three months of principal and interest payments under the Assistance Agreement, beginning with the May 2020 payment. These deferred payments will be added at the end of the loan, thus extending out the maturity date by three months.
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] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of loan forgiveness											5.00%
State of Connecticut [Member] | Second Amendment [Member] | Employment Obligation [Member]
Debt Instrument [Line Items]
Number of minimum full time positions required to be maintained | Position								538
Number of consecutive months maintain full time positions								24 months
Additional number of full time positions required to be create | Position								91
Additional credits to be earned								$ 2,000,000.0
Target date of job audit								90 days
Principal payable number of employee under employee obligation target								$ 18,587.36
Liberty Bank Promissory Note (PPP Note) [Member]
Debt Instrument [Line Items]
Long-term line of credit										6,515,000	$ 6,515,000
Long-term Line of Credit										$ 6,515,000	$ 6,515,000
Proceeds from long-term lines of credit	$ 6,500,000
Liberty Bank Promissory Note (PPP Note) [Member] | Liberty Bank [Member] | CARES Act [Member]
Debt Instrument [Line Items]
Maturity date											Apr. 16, 2022
Loan forgiveness terms											The loan may be fully forgiven if (i) proceeds are used to pay eligible payroll costs, rent, mortgage interest and utilities and (ii) full-time employee headcount and salaries are either maintained during the 24-week period following disbursement or restored by December 31, 2020. If not so maintained or restored, any forgiveness of the loan would be reduced in accordance with the regulations that were issued by the SBA.
Debt instrument, interest rate, stated percentage rate range											1.00%
Debt instrument, collateral or guarantees											The Company did not provide any collateral or guarantees for the PPP Note, nor did the Company pay any facility charge to obtain the PPP Note.
Prepayment penalties											$ 0
Proceeds used for payroll costs on an annualized basis for each employee											$ 100,000
New Britain Renewable Energy Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage rate range											5.00%
Notes payable to bank, current												500,000
Enhanced Capital Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Long-term line of credit												1,500,000
Line of credit facility, maximum borrowing capacity					$ 1,500,000
Long-term Line of Credit												1,500,000
Interest rate, basis points					6.00%
New Construction Loan Facility [Member] | Fifth Third Bank Groton Loan [Member]
Debt Instrument [Line Items]
Total outstanding balance				$ 11,100
New Construction Loan Facility [Member] | Fifth Third Bank Groton Loan [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				23,000,000.0								$ 18,000,000.0
Loan advance				$ 9,700,000			$ 1,400,000
New Construction Loan Facility [Member] | Fifth Third Bank Groton Loan [Member] | Groton CT [Member]
Debt Instrument [Line Items]
Capacity of plant | MW				7.4
PNC Energy Capital, LLC [Member]
Debt Instrument [Line Items]
Debt instrument term											10 years
Bridgeport Fuel Cell, LLC [Member]
Debt Instrument [Line Items]
Debt instrument term											8 years
Orion Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument term											8 years