Guarantor financial information - Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Jul. 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2018
Revenues:
Revenues	$ 281,649	$ 412,130	$ 510,833	$ 293,214	$ 279,081	$ 479,625	$ 573,377	$ 352,309	$ 347,521	$ 515,810	$ 755,156	$ 454,655	$ 1,497,826	$ 1,684,392	$ 2,073,142
Costs and expenses:
Operating expense - personnel, vehicle, plant and other													493,055	468,868	471,748
Operating expense - equipment lease expense													33,017
Equipment lease expense, preadoption														33,073	28,272
Depreciation and amortization expense													80,481	78,846	101,795
General and administrative expense													45,752	59,994	54,401
Non-cash employee stock ownership plan compensation charge													2,871	5,693	13,859
Asset impairments											10,000		0	0	10,005
Loss on asset sales and disposals													7,924	10,968	187,399
Operating income													148,670	113,028	(91,964)
Interest expense													(192,962)	(177,619)	(168,467)
Loss on extinguishment of debt		(37,400)											(37,399)
Other income (expense), net													(460)	369	928
Loss before income taxes													(82,151)	(64,222)	(259,503)
Income tax expense (benefit)													851	323	(2,678)
Net loss	(70,605)	(15,471)	48,791	(45,717)					(217,797)	11,062	(1,774)	(48,316)	(83,002)	(64,545)	(256,825)
Other comprehensive income (loss)													12,334	(35,380)	5,969
Comprehensive loss													(70,668)	(99,925)	(250,856)
Propane [Member]
Revenues:
Revenues													1,415,791	1,608,858	1,642,976
Costs and expenses:
Cost of sales													673,053	902,516	973,414
Midstream Operations [Member]
Revenues:
Revenues															282,319
Costs and expenses:
Cost of sales															255,559
Other Revenues
Revenues:
Revenues													82,035	75,534	147,847
Costs and expenses:
Cost of sales													13,003	11,406	68,654
Parent Company [Member]
Costs and expenses:
General and administrative expense													116	14	137
Operating income													(49,377)	(29,233)	(220,039)
Interest expense													(33,073)	(34,984)	(34,521)
Income tax expense (benefit)													49	30	21
Equity in earnings (loss) of Ferrellgas, L.P.													(49,261)	(29,219)	(219,902)
Net loss													(82,499)	(64,247)	(254,581)
Reportable Legal Entities [Member] | Parent Company [Member]
Revenues:
Revenues													1,497,826	1,684,343
Costs and expenses:
Operating expense - personnel, vehicle, plant and other													493,055	469,652	436,962
Operating expense - equipment lease expense													33,017
Equipment lease expense, preadoption														33,073	27,939
Depreciation and amortization expense													80,025	78,400	75,163
General and administrative expense													45,630	59,974	48,337
Non-cash employee stock ownership plan compensation charge													2,871	5,693	13,859
Asset impairments															0
Loss on asset sales and disposals													7,924	8,289	8,978
Operating income													149,248	115,454	121,293
Interest expense													(156,286)	(132,929)	(86,646)
Loss on extinguishment of debt													(37,399)
Other income (expense), net													(360)	428	(234)
Loss before income taxes													(44,797)	(17,047)	34,413
Income tax expense (benefit)													802	105	222
Equity in earnings (loss) of Ferrellgas, L.P.													(2,444)	(12,365)	(256,337)
Net loss													(48,043)	(29,517)	(222,146)
Other comprehensive income (loss)													12,334	(35,380)	5,969
Comprehensive loss													(35,709)	(64,897)	(216,177)
Reportable Legal Entities [Member] | Parent Company [Member] | Propane [Member]
Revenues:
Revenues													1,415,791	1,608,858
Costs and expenses:
Cost of sales													673,053	902,516	972,467
Reportable Legal Entities [Member] | Parent Company [Member] | Midstream Operations [Member]
Costs and expenses:
Cost of sales															0
Reportable Legal Entities [Member] | Parent Company [Member] | Other Revenues
Revenues:
Revenues													82,035	75,485
Costs and expenses:
Cost of sales													13,003	11,292	10,111
Reportable Legal Entities [Member] | Subsidiary Issuer [Member]
Revenues:
Revenues													0	0
Costs and expenses:
Operating expense - personnel, vehicle, plant and other													0	0	0
Operating expense - equipment lease expense													0
Equipment lease expense, preadoption														0	0
Depreciation and amortization expense													0	0	0
General and administrative expense													6	6	5
Non-cash employee stock ownership plan compensation charge													0	0	0
Asset impairments															0
Loss on asset sales and disposals													0	0	0
Operating income													(6)	(6)	(5)
Interest expense													0	0	0
Loss on extinguishment of debt													0
Other income (expense), net													0	0	0
Loss before income taxes													(6)	(6)	(5)
Income tax expense (benefit)													0	0	0
Equity in earnings (loss) of Ferrellgas, L.P.													0	0	0
Net loss													(6)	(6)	(5)
Other comprehensive income (loss)													0	0	0
Comprehensive loss													(6)	(6)	(5)
Reportable Legal Entities [Member] | Subsidiary Issuer [Member] | Propane [Member]
Revenues:
Revenues													0	0
Costs and expenses:
Cost of sales													0	0	0
Reportable Legal Entities [Member] | Subsidiary Issuer [Member] | Midstream Operations [Member]
Costs and expenses:
Cost of sales															0
Reportable Legal Entities [Member] | Subsidiary Issuer [Member] | Other Revenues
Revenues:
Revenues													0	0
Costs and expenses:
Cost of sales													0	0	0
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Revenues:
Revenues													0	49
Costs and expenses:
Operating expense - personnel, vehicle, plant and other													0	37	37,617
Operating expense - equipment lease expense													0
Equipment lease expense, preadoption														0	333
Depreciation and amortization expense													0	0	26,317
General and administrative expense													0	0	5,922
Non-cash employee stock ownership plan compensation charge													0	0	0
Asset impairments															10,005
Loss on asset sales and disposals													0	2,679	178,421
Operating income													0	(2,781)	(215,631)
Interest expense													0	(38)	(43,247)
Loss on extinguishment of debt													0
Other income (expense), net													(100)	(59)	1,162
Loss before income taxes													(100)	(2,878)	(257,716)
Income tax expense (benefit)													0	188	(2,921)
Equity in earnings (loss) of Ferrellgas, L.P.													0	0	0
Net loss													(100)	(3,066)	(254,795)
Other comprehensive income (loss)													0	0	0
Comprehensive loss													(100)	(3,066)	(254,795)
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Propane [Member]
Revenues:
Revenues													0	0
Costs and expenses:
Cost of sales													0	0	947
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Midstream Operations [Member]
Costs and expenses:
Cost of sales															255,559
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Other Revenues
Revenues:
Revenues													0	49
Costs and expenses:
Cost of sales													0	114	58,543
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Revenues:
Revenues													0	0
Costs and expenses:
Operating expense - personnel, vehicle, plant and other													3,950	3,589	4,755
Operating expense - equipment lease expense													0
Equipment lease expense, preadoption														0	0
Depreciation and amortization expense													456	446	315
General and administrative expense													0	0	0
Non-cash employee stock ownership plan compensation charge													0	0	0
Asset impairments															0
Loss on asset sales and disposals													0	0	0
Operating income													(4,406)	(4,035)	(5,070)
Interest expense													(3,603)	(9,668)	(4,053)
Loss on extinguishment of debt													0
Other income (expense), net													5,671	4,410	7,586
Loss before income taxes													(2,338)	(9,293)	(1,537)
Income tax expense (benefit)													0	0	0
Equity in earnings (loss) of Ferrellgas, L.P.													0	0	0
Net loss													(2,338)	(9,293)	(1,537)
Other comprehensive income (loss)													0	0	0
Comprehensive loss													(2,338)	(9,293)	(1,537)
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member] | Propane [Member]
Revenues:
Revenues													0	0
Costs and expenses:
Cost of sales													0	0	0
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member] | Midstream Operations [Member]
Costs and expenses:
Cost of sales															0
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member] | Other Revenues
Revenues:
Revenues													0	0
Costs and expenses:
Cost of sales													0	0	0
Eliminations [Member]
Revenues:
Revenues													0	0
Costs and expenses:
Operating expense - personnel, vehicle, plant and other													(3,950)	(4,410)	(7,586)
Operating expense - equipment lease expense													0
Equipment lease expense, preadoption														0	0
Depreciation and amortization expense													0	0	0
General and administrative expense													0	0	0
Non-cash employee stock ownership plan compensation charge													0	0	0
Asset impairments															0
Loss on asset sales and disposals													0	0	0
Operating income													3,950	4,410	7,586
Interest expense													0	0	0
Loss on extinguishment of debt													0
Other income (expense), net													(5,671)	(4,410)	(7,586)
Loss before income taxes													(1,721)	0	0
Income tax expense (benefit)													0	0	0
Equity in earnings (loss) of Ferrellgas, L.P.													2,444	12,365	256,337
Net loss													723	12,365	256,337
Other comprehensive income (loss)													0	0	0
Comprehensive loss													723	12,365	256,337
Eliminations [Member] | Propane [Member]
Revenues:
Revenues													0	0
Costs and expenses:
Cost of sales													0	0	0
Eliminations [Member] | Midstream Operations [Member]
Costs and expenses:
Cost of sales															0
Eliminations [Member] | Other Revenues
Revenues:
Revenues													0	0
Costs and expenses:
Cost of sales													0	0	0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Other Revenues
Revenues:
Revenues														75,534	147,847
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Parent Company [Member]
Revenues:
Revenues															1,715,109
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Parent Company [Member] | Propane [Member]
Revenues:
Revenues															1,642,155
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Parent Company [Member] | Midstream Operations [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Parent Company [Member] | Other Revenues
Revenues:
Revenues															72,954
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Subsidiary Issuer [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Subsidiary Issuer [Member] | Propane [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Subsidiary Issuer [Member] | Midstream Operations [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Subsidiary Issuer [Member] | Other Revenues
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Revenues:
Revenues															358,033
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Propane [Member]
Revenues:
Revenues															821
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Midstream Operations [Member]
Revenues:
Revenues															282,319
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Other Revenues
Revenues:
Revenues															74,893
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member] | Propane [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member] | Midstream Operations [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member] | Other Revenues
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Eliminations [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Eliminations [Member] | Propane [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Eliminations [Member] | Midstream Operations [Member]
Revenues:
Revenues															0
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Eliminations [Member] | Other Revenues
Revenues:
Revenues															0
Ferrellgas, L.P. [Member]
Revenues:
Revenues	281,649	412,130	510,833	293,214	279,081	479,625	573,377	352,309	347,521	515,810	755,156	454,655	1,497,826	1,684,392	2,073,142
Costs and expenses:
Operating expense - personnel, vehicle, plant and other													493,055	468,868	471,748
Operating expense - equipment lease expense													33,017
Equipment lease expense, preadoption														33,073	28,272
Depreciation and amortization expense													80,481	78,846	101,795
General and administrative expense													45,636	59,980	54,264
Non-cash employee stock ownership plan compensation charge													2,871	5,693	13,859
Asset impairments											10,000				10,005
Loss on asset sales and disposals													7,924	10,968	187,399
Operating income													148,786	113,042	(91,827)
Interest expense													(159,889)	(142,635)	(133,946)
Loss on extinguishment of debt		(37,400)											(37,399)
Other income (expense), net													(460)	369	928
Loss before income taxes													(48,962)	(29,224)	(224,845)
Income tax expense (benefit)													802	293	(2,699)
Equity in earnings (loss) of Ferrellgas, L.P.													0	0	0
Net loss	$ (62,902)	$ (7,720)	$ 57,756	$ (36,898)	$ (62,874)	$ 29,554	$ 52,617	$ (48,814)	$ (209,134)	$ 19,840	$ 6,847	$ (39,699)	(49,764)	(29,517)	(222,146)
Other comprehensive income (loss)													12,334	(35,380)	5,969
Comprehensive loss													(37,430)	(64,897)	(216,177)
Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues													1,415,791	1,608,858	1,642,976
Costs and expenses:
Cost of sales													673,053	902,516	973,414
Ferrellgas, L.P. [Member] | Midstream Operations [Member]
Revenues:
Revenues															282,319
Costs and expenses:
Cost of sales															255,559
Ferrellgas, L.P. [Member] | Other Revenues
Revenues:
Revenues													82,035	75,534	147,847
Costs and expenses:
Cost of sales													$ 13,003	11,406	68,654
Ferrellgas, L.P. [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenues:
Revenues															2,073,142
Ferrellgas, L.P. [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Propane [Member]
Revenues:
Revenues															1,642,976
Ferrellgas, L.P. [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Midstream Operations [Member]
Revenues:
Revenues															282,319
Ferrellgas, L.P. [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Other Revenues
Revenues:
Revenues														$ 75,534	$ 147,847