Guarantor financial information - Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jan. 31, 2020	Oct. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Jan. 31, 2020	Jan. 31, 2019
Revenues:
Revenues	$ 510,833		$ 573,377		$ 804,047	$ 925,686
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	128,233		121,219		242,776	231,550
Depreciation and amortization expense	19,795		19,605		39,014	38,597
General and administrative expense	14,192		16,342		23,887	30,521
Operating expense - equipment lease expense	8,261				16,649
Equipment lease expense, preadoption			8,415			16,278
Non-cash employee stock ownership plan compensation charge	630		1,944		1,425	4,692
Loss on asset sales and disposals	2,148		2,216		4,383	6,720
Operating Income (Loss)	96,378		88,683		97,008	75,192
Interest expense	(47,548)		(44,891)		(93,245)	(88,769)
Other income (expense), net	76		86		(56)	105
Earnings (loss) before income taxes	48,906		43,878		3,707	(13,472)
Income tax expense (benefit)	115		3		633	161
Net earnings (loss)	48,791	$ (45,717)	43,875	$ (57,508)	3,074	(13,633)
Other comprehensive loss	(2,555)	(6,148)	(17,273)	(12,587)	(8,703)	(29,860)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	46,236		26,602		(5,629)	(43,493)
Propane [Member]
Revenues:
Revenues	485,247		550,112		758,632	885,078
Costs and expenses:
Cost of sales	237,843		311,531		371,871	515,667
Other Revenues
Revenues:
Revenues	25,586		23,265		45,415	40,608
Costs and expenses:
Cost of sales	3,353		3,422		7,034	6,469
Ferrellgas, L.P. [Member]
Revenues:
Revenues	510,833		573,377		804,047	925,686
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	128,233		121,219		242,776	231,550
Depreciation and amortization expense	19,795		19,605		39,014	38,597
General and administrative expense	14,085		16,341		23,781	30,516
Operating expense - equipment lease expense	8,261				16,649
Equipment lease expense, preadoption			8,415			16,278
Non-cash employee stock ownership plan compensation charge	630		1,944		1,425	4,692
Loss on asset sales and disposals	2,148		2,216		4,383	6,720
Operating Income (Loss)	96,485		88,684		97,114	75,197
Interest expense	(38,690)		(36,150)		(75,567)	(71,345)
Other income (expense), net	76		86		(56)	105
Earnings (loss) before income taxes	57,871		52,620		21,491	3,957
Income tax expense (benefit)	115		3		633	154
Net earnings (loss)	57,756	(36,898)	52,617	(48,814)	20,858	3,803
Other comprehensive loss	(2,555)	$ (6,148)	(17,273)	$ (12,587)	(8,703)	(29,860)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	55,201		35,344		12,155	(26,057)
Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues	485,247		550,112		758,632	885,078
Costs and expenses:
Cost of sales	237,843		311,531		371,871	515,667
Ferrellgas, L.P. [Member] | Other Revenues
Revenues:
Revenues	25,586		23,265		45,415	40,608
Costs and expenses:
Cost of sales	3,353		3,422		7,034	6,469
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues	510,833				804,047
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	128,233		121,180		242,776	231,511
Depreciation and amortization expense	19,684		19,493		38,791	38,374
General and administrative expense	14,082		16,338		23,777	30,511
Operating expense - equipment lease expense	8,261				16,649
Equipment lease expense, preadoption			8,415			16,278
Non-cash employee stock ownership plan compensation charge	630		1,944		1,425	4,692
Loss on asset sales and disposals	2,148		2,045		4,383	4,041
Operating Income (Loss)	96,599		89,074		97,341	78,208
Interest expense	(37,778)		(34,655)		(73,469)	(69,003)
Other income (expense), net	76		96		(56)	115
Earnings (loss) before income taxes	58,897		54,515		23,816	9,320
Income tax expense (benefit)	115		3		633	154
Equity in earnings (loss) of Ferrellgas, L.P.	(194)		(863)		(1,658)	(3,145)
Net earnings (loss)	58,588		53,649		21,525	6,021
Other comprehensive loss	(2,555)		(17,273)		(8,703)	(29,860)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	56,033		36,376		12,822	(23,839)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Propane [Member]
Revenues:
Revenues	485,247				758,632
Costs and expenses:
Cost of sales	237,843				371,871
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Other Revenues
Revenues:
Revenues	25,586				45,415
Costs and expenses:
Cost of sales	3,353				7,034
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Subsidiary Issuer [Member]
Costs and expenses:
General and administrative expense	3		3		4	5
Operating Income (Loss)	(3)		(3)		(4)	(5)
Earnings (loss) before income taxes	(3)		(3)		(4)	(5)
Net earnings (loss)	(3)		(3)		(4)	(5)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(3)		(3)		(4)	(5)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other			39			39
Loss on asset sales and disposals			171			2,679
Operating Income (Loss)			(275)			(2,783)
Interest expense			(38)			(38)
Other income (expense), net			(10)			(10)
Earnings (loss) before income taxes			(323)			(2,831)
Net earnings (loss)			(323)			(2,831)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest			(323)			(2,831)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	1,050		1,884		1,935	2,901
Depreciation and amortization expense	111		112		223	223
Operating Income (Loss)	(1,161)		(1,996)		(2,158)	(3,124)
Interest expense	(912)		(1,457)		(2,098)	(2,304)
Other income (expense), net	1,882		2,916		2,602	5,119
Earnings (loss) before income taxes	(191)		(537)		(1,654)	(309)
Net earnings (loss)	(191)		(537)		(1,654)	(309)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(191)		(537)		(1,654)	(309)
Eliminations [Member] | Ferrellgas, L.P. [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	(1,050)		(1,884)		(1,935)	(2,901)
Operating Income (Loss)	1,050		1,884		1,935	2,901
Other income (expense), net	(1,882)		(2,916)		(2,602)	(5,119)
Earnings (loss) before income taxes	(832)		(1,032)		(667)	(2,218)
Equity in earnings (loss) of Ferrellgas, L.P.	194		863		1,658	3,145
Net earnings (loss)	(638)		(169)		991	927
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ (638)		(169)		$ 991	927
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Other Revenues
Revenues:
Revenues			23,265			40,608
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member]
Revenues:
Revenues			573,377			925,686
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues			550,112			885,078
Costs and expenses:
Cost of sales			311,531			515,667
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Other Revenues
Revenues:
Revenues			23,265			40,608
Costs and expenses:
Cost of sales			3,422			6,469
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues			573,328			925,637
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Propane [Member]
Revenues:
Revenues			550,112			885,078
Costs and expenses:
Cost of sales			311,531			515,667
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Other Revenues
Revenues:
Revenues			23,216			40,559
Costs and expenses:
Cost of sales			3,308			6,355
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Revenues:
Revenues			49			49
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member] | Other Revenues
Revenues:
Revenues			49			49
Costs and expenses:
Cost of sales			$ 114			$ 114