Debt and Financing Obligations - Additional Information (Details) $ / shares in Units, shares in Millions									1 Months Ended			3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 17, 2020 USD ($)	Jun. 05, 2020	Apr. 24, 2020 USD ($)	Apr. 20, 2020	Feb. 11, 2020 USD ($)	Nov. 22, 2019 USD ($) $ / shares MW shares	May 09, 2019 USD ($) MW	Feb. 28, 2019 USD ($) MW	Apr. 30, 2019 USD ($)	Jan. 31, 2019 USD ($) Position Employee	Oct. 31, 2015 USD ($) Position	Apr. 30, 2020 USD ($)	Jan. 31, 2020 USD ($)	Apr. 30, 2019 USD ($)	Jan. 31, 2019 USD ($)	Apr. 30, 2020 USD ($) MW	Apr. 30, 2019 USD ($)	Apr. 30, 2020 USD ($)	Oct. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	May 16, 2019	May 08, 2019	Feb. 06, 2019 USD ($)	Jan. 09, 2019 USD ($)	Nov. 30, 2016 USD ($)
Debt Instrument [Line Items]
Long-term line of credit, discount												$ 5,520,000				$ 5,520,000		$ 5,520,000	$ 4,251,000
Class of warrants or rights issued value																			$ 3,900,000
Dividends declared												800,000	$ 931,000	$ 800,000	$ 800,000
Series B Preferred Stock [Member]
Debt Instrument [Line Items]
Dividends declared												800,000		$ 800,000		1,731,000	$ 1,600,000
Third Orion Amendment [Member]
Debt Instrument [Line Items]
Taxes and transaction costs					$ 1,000,000.0
Proceeds from sale leaseback transferred to module reserve account					1,100,000
Proceeds from sale leaseback transferred to debt reserve account					100,000
Quarterly cash interest due to the lenders					1,700,000
Long-term restricted cash												6,500,000				6,500,000		6,500,000
Third Orion Amendment [Member] | Series B Preferred Stock [Member]
Debt Instrument [Line Items]
Dividends declared					$ 1,100,000
Third Orion Amendment [Member] | Maximum [Member]
Debt Instrument [Line Items]
Allocate of fund to project																3,500,000
Fourth Orion Amendment [Member]
Debt Instrument [Line Items]
Release of funds from project proceeds account subject to conditions																3,500,000
Project payoff amount																5,000,000
Release of funds from project proceeds account transferred to covered project account																1,200,000
Self-generation incentive program amount, granted																$ 1,000,000.0
Fourth Orion Amendment [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Release of funds from project proceeds account subject to conditions	$ 3,500,000
Release of funds from project proceeds account transferred to general business unit account	$ 2,300,000
Fourth Orion Amendment [Member] | California [Member]
Debt Instrument [Line Items]
Capacity of plant | MW																1.4
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
Proceeds from long-term lines of credit																$ 18,600,000			0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Groton CT [Member]
Debt Instrument [Line Items]
Disposition,refinancing or tax equity investment consummated																30,000,000
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Tulare BioMAT [Member]
Debt Instrument [Line Items]
Disposition,refinancing or tax equity investment consummated																$ 5,000,000.0
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
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
Debt instrument term																7 years
Quarterly payment payable period																1 year
Quarterly payment payable date																Oct. 31, 2027
Debt instrument, description																Outstanding principal under the Orion Facility will be amortized on a straight-line basis over a seven year term in quarterly payments beginning one year after the Initial Funding, with the initial payment due 21 business days after the end of the first quarter of fiscal 2021; provided that, if the Company does not have sufficient cash on hand to make any required quarterly amortization payments, such amounts shall be deferred and payable at such time as sufficient cash is available to make such payments subject to all outstanding principal being due and payable on the maturity date, which is the date that is eight years after the date of the Initial Funding or October 31, 2027.
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
Credit agreement requires to establish debt reserve												5,000,000.0				$ 5,000,000.0		5,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member] | Exercise Price 0.242 [Member]
Debt Instrument [Line Items]
Class of warrants or rights exercised | shares						8.0
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 0.242
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member] | Exercise Price 0.620 [Member]
Debt Instrument [Line Items]
Class of warrants or rights exercised | shares						6.0
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 0.620
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						14.0
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] | Remainder of Funding [Member]
Debt Instrument [Line Items]
Line of credit receivable amount																			120,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Remainder of Funding [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit receivable amount												120,000,000.0				120,000,000.0		120,000,000.0
Connecticut Green Bank Loans [Member]
Debt Instrument [Line Items]
Long-term Line of Credit												4,800,000				4,800,000		$ 4,800,000
Line of credit facility, maximum borrowing capacity																			1,800,000	$ 3,000,000.0
Accrued fees payable							$ 400,000
Debt instrument, interest rate, stated percentage rate																						5.00%
Debt instrument, interest rate, increase																		8.00%
Connecticut Green Bank Loans [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												5,400,000				$ 5,400,000		$ 5,400,000
Capacity of plant | MW							14.9
Debt instrument, interest rate, stated percentage rate							8.00%
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 representations, warranties and covenants. The balance under the Subordinated Credit Agreement as of April 30, 2020 was $5.4 million.
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							1,800,000
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
Subordinated Credit Agreement [Member] | Previously Received [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
Credit Agreement [Member] | Bridgeport Loans [Member]
Debt Instrument [Line Items]
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 [Member] | Bridgeport Loans [Member] | Interest Rate Swap
Debt Instrument [Line Items]
Net interest rate																					5.09%
Credit Agreement [Member] | Bridgeport Loans [Member] | Level Adjustments [Member] | Interest Rate Swap
Debt Instrument [Line Items]
Fair value adjustments, charge												500,000				$ 500,000
Fair value interest rate												1,200,000				1,200,000		1,200,000	600,000
Credit Agreement [Member] | Bridgeport Fuel Cell, LLC [Member]
Debt Instrument [Line Items]
Debt instrument, total notional value							$ 25,000,000.0
Credit Agreement [Member] | 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 [Member] | 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
Finance Obligations for Sale Leaseback Agreements [Member] | PNC Energy Capital, LLC [Member]
Debt Instrument [Line Items]
Long-term Line of Credit												55,700,000				55,700,000		55,700,000	45,200,000
State of Connecticut [Member]
Debt Instrument [Line Items]
Long-term Line of Credit												9,660,000				9,660,000		9,660,000	10,000,000
Debt instrument term											15 years
Debt instrument, interest rate, stated percentage rate											2.00%
Debt instrument, total notional value											$ 10,000,000.0	10,000,000.0				$ 10,000,000.0		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 | 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										$ 2,000,000.0					2,000,000.0
Target date of job audit										90 days
Principal payable number of employee under employee obligation target										$ 18,587.36					$ 18,587.36
Webster Bank Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage rate range																5.00%
Notes payable to bank, current																			500,000						$ 2,300,000
Enhanced Capital Term 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
New Construction Loan Facility [Member] | Fifth Third Bank Groton Loan [Member]
Debt Instrument [Line Items]
Total outstanding balance																			$ 11,100,000
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
Loan advance								$ 9,700,000	$ 1,400,000
New Construction Loan Facility [Member] | Groton CT [Member] | Fifth Third Bank Groton Loan [Member]
Debt Instrument [Line Items]
Capacity of plant | MW								7.4
Liberty Bank Promissory Note (PPP Note) [Member]
Debt Instrument [Line Items]
Long-term Line of Credit												$ 6,515,000				$ 6,515,000		$ 6,515,000
Liberty Bank Promissory Note (PPP Note) [Member] | Liberty Bank [Member]
Debt Instrument [Line Items]
Loan forgiveness terms																In order to obtain the consent of the Agent and the Orion Lenders under the Orion Facility to enter into the PPP Note, the Agent and the Orion Lenders have required the Company to apply for forgiveness within 30 days after the last day of the loan forgiveness period as designated under the PPP regulations in effect as of June 6, 2020.
Liberty Bank Promissory Note (PPP Note) [Member] | Liberty Bank [Member] | CARES Act [Member]
Debt Instrument [Line Items]
Debt instrument term			2 years	2 years
Proceeds from long-term lines of credit			$ 6,500,000
Maturity date																Apr. 16, 2022
Loan forgiveness terms																In order to obtain the consent of the Agent and the Orion Lenders under the Orion Facility to enter into the PPP Note, the Agent and the Orion Lenders have required the Company to apply for forgiveness within 30 days after the last day of the loan forgiveness period as designated under the PPP regulations in effect as of June 6, 2020. If we seek forgiveness of the loan, we must apply for such forgiveness by October 31, 2020.
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
Loan forgiveness period			56 days	56 days
Liberty Bank Promissory Note (PPP Note) [Member] | Subsequent Event [Member] | Liberty Bank [Member] | PPP Flexibility Act [Member]
Debt Instrument [Line Items]
Debt instrument term		5 years
Loan forgiveness period		168 days
Liberty Bank Promissory Note (PPP Note) [Member] | Minimum [Member] | Liberty Bank [Member] | CARES Act [Member]
Debt Instrument [Line Items]
Percentage of proceeds used for payroll costs			75.00%	75.00%												75.00%
Liberty Bank Promissory Note (PPP Note) [Member] | Minimum [Member] | Subsequent Event [Member] | Liberty Bank [Member] | PPP Flexibility Act [Member]
Debt Instrument [Line Items]
Percentage of proceeds used for payroll costs		60.00%
PNC and Crestmark [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