Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Series C Preferred Stock [Member]	Series D Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Series C Preferred Stock [Member]	Additional Paid-in Capital [Member] Series D Preferred Stock [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member] Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Deferred Compensation [Member]
Balance at Oct. 31, 2018	$ 82,194				$ 1	$ 1,073,463			$ (990,867)		$ (403)	$ (363)	$ 363
Balance at (in shares) at Oct. 31, 2018					7,972,686
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share based compensation	987					987
Fee adjustment for common stock issuance	90					90
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans	27					27
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans, (in shares)					1,946
Series C convertible preferred stock conversions	1,974					1,974
Series C convertible preferred stock conversions, (in shares)					127,829
Series C convertible preferred stock modification				$ (3,793)				$ (3,793)
Series C convertible preferred stock adjustment for beneficial conversion feature	6,586					6,586
Series C convertible stock redemption value adjustments	(8,550)					(8,550)
Series D convertible preferred stock conversions	4,334					4,334
Series D convertible preferred stock conversions, (in shares)					932,144
Preferred dividends — Series B	(800)					(800)
Effect of foreign currency translation	7										7
Net loss attributable to FuelCell Energy, Inc.	(17,548)								(17,548)
Balance at Jan. 31, 2019	58,854	$ (6,654)			$ 1	1,074,318			(1,015,069)	$ (6,654)	(396)	(363)	363
Balance at (in shares) at Jan. 31, 2019					9,034,605
Balance at Oct. 31, 2018	82,194				$ 1	1,073,463			(990,867)		(403)	(363)	363
Balance at (in shares) at Oct. 31, 2018					7,972,686
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of foreign currency translation	(28)
Net loss attributable to FuelCell Energy, Inc.	(42,389)
Balance at Jul. 31, 2019	84,883				$ 12	1,125,212			(1,039,910)		(431)	(466)	466
Balance at (in shares) at Jul. 31, 2019					118,387,637
Balance at Jan. 31, 2019	58,854	$ (6,654)			$ 1	1,074,318			(1,015,069)	$ (6,654)	(396)	(363)	363
Balance at (in shares) at Jan. 31, 2019					9,034,605
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued, non-employee compensation	102					102
Common stock issued, non-employee compensation, (in shares)					29,454
Share based compensation	955					955
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans	(219)					(219)
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans, (in shares)					52,784
Series A warrant exchange, shares					500,000
Series C convertible preferred stock conversions	10,355					10,355
Series C convertible preferred stock conversions, (in shares)					2,127,528
Series C convertible preferred stock modification			$ (6,047)				$ (6,047)
Series D convertible preferred stock conversions	6,305					6,305
Series D convertible preferred stock conversions, (in shares)					1,994,413
Preferred dividends — Series B	(800)					(800)
Adjustment for deferred compensation													103
Adjustment for deferred compensation, (in shares)					(29,454)
Adjustment for deferred compensation												(103)
Effect of foreign currency translation	(140)										(140)
Net loss attributable to FuelCell Energy, Inc.	(19,530)								(19,530)
Balance at Apr. 30, 2019	49,835				$ 1	1,084,969			(1,034,599)		(536)	(466)	466
Balance at (in shares) at Apr. 30, 2019					13,709,330
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share based compensation	383					383
Sale of common stock, net of fees	16,199				$ 3	16,196
Sale of common stock, net of fees (in shares)					43,997,807
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans	(9)					(9)
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans, (in shares)					437
Series C convertible preferred stock conversions	3,162				$ 2	3,160
Series C convertible preferred stock conversions, (in shares)					1,658,861
Series D convertible preferred stock conversions	20,519				$ 6	20,513
Series D convertible preferred stock conversions, (in shares)					59,021,202
Effect of foreign currency translation	105										105
Net loss attributable to FuelCell Energy, Inc.	(5,311)								(5,311)
Balance at Jul. 31, 2019	84,883				$ 12	1,125,212			(1,039,910)		(431)	(466)	466
Balance at (in shares) at Jul. 31, 2019					118,387,637
Balance at Oct. 31, 2019	$ 75,737				$ 19	1,151,454			(1,075,089)		(647)	(466)	466
Balance at (in shares) at Oct. 31, 2019	193,608,684				193,608,684
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share based compensation	$ 488					488
Orion warrant exercises	25,994				$ 1	25,993
Orion warrant exercises, shares					9,396,320
Sale of common stock, net of fees	3,502				$ 1	3,501
Sale of common stock, net of fees (in shares)					7,938,228
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans	(6)					(6)
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans, (in shares)					2,585
Preferred dividends — Series B	(931)					(931)
Adjustment for deferred compensation													(29)
Adjustment for deferred compensation, (in shares)					20,012
Adjustment for deferred compensation												29
Effect of foreign currency translation	(49)										(49)
Net loss attributable to FuelCell Energy, Inc.	(40,151)								(40,151)
Balance at Jan. 31, 2020	64,584				$ 21	1,180,499			(1,115,240)		(696)	(437)	437
Balance at (in shares) at Jan. 31, 2020					210,965,829
Balance at Oct. 31, 2019	$ 75,737				$ 19	1,151,454			(1,075,089)		(647)	(466)	466
Balance at (in shares) at Oct. 31, 2019	193,608,684				193,608,684
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of foreign currency translation	$ (230)
Net loss attributable to FuelCell Energy, Inc.	(70,251)
Balance at Jul. 31, 2020	$ 96,325				$ 24	1,242,518			(1,145,340)		(877)	(403)	403
Balance at (in shares) at Jul. 31, 2020	236,172,797				236,172,797
Balance at Jan. 31, 2020	$ 64,584				$ 21	1,180,499			(1,115,240)		(696)	(437)	437
Balance at (in shares) at Jan. 31, 2020					210,965,829
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share based compensation	375					375
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans	(32)					(32)
Taxes paid upon vesting of restricted stock awards, net of stock issued under benefit plans, (in shares)					86,572
Preferred dividends — Series B	(800)					(800)
Effect of foreign currency translation	(42)										(42)
Net loss attributable to FuelCell Energy, Inc.	(14,769)								(14,769)
Balance at Apr. 30, 2020	49,316				$ 21	1,180,042			(1,130,009)		(738)	(437)	437
Balance at (in shares) at Apr. 30, 2020					211,052,401
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued, non-employee compensation	112					112
Common stock issued, non-employee compensation, (in shares)					(8,272)
Reclassification of value of share based compensation upon approval of authorized shares for grant	434					434
Share based compensation	398					398
Sale of common stock, net of fees	62,331				$ 3	62,328
Sale of common stock, net of fees (in shares)					25,144,704
Stock issued under benefit plans, net of taxes paid upon vesting of restricted stock awards	4					4
Stock issued under benefit plans, net of taxes paid upon vesting of restricted stock awards, (in shares)					2,150
Preferred dividends — Series B	(800)					(800)
Adjustment for deferred compensation													(34)
Adjustment for deferred compensation, (in shares)					(18,186)
Adjustment for deferred compensation												34
Effect of foreign currency translation	(139)										(139)
Net loss attributable to FuelCell Energy, Inc.	(15,331)								(15,331)
Balance at Jul. 31, 2020	$ 96,325				$ 24	$ 1,242,518			$ (1,145,340)		$ (877)	$ (403)	$ 403
Balance at (in shares) at Jul. 31, 2020	236,172,797				236,172,797