Guarantor financial information - Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jan. 31, 2021	Oct. 31, 2020	Jan. 31, 2020	Oct. 31, 2019	Jan. 31, 2021	Jan. 31, 2020
Revenues:
Revenues	$ 553,560		$ 510,833		$ 854,454	$ 804,047
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	115,247		128,233		224,274	242,776
Operating expense - equipment lease expense	6,862		8,261		13,692	16,649
Depreciation and amortization expense	21,249		19,795		42,639	39,014
General and administrative expense	20,475		14,192		33,555	23,887
Non-cash employee stock ownership plan compensation charge	762		630		1,470	1,425
Loss on asset sales and disposals	80		2,148		893	4,383
Operating income	114,604		96,378		122,356	97,008
Interest expense	(52,595)		(47,548)		(106,821)	(93,245)
Other income (expense), net	3,508		76		3,616	(56)
Earnings (loss) before income taxes	64,317		48,906		17,951	3,707
Income tax expense (benefit)	326		115		413	633
Net earnings (loss)	63,991	$ (46,453)	48,791	$ (45,717)	17,538	3,074
Other comprehensive income (loss)	28,516	7,917	(2,555)	(6,148)	36,433	(8,703)
Comprehensive loss	92,507		46,236		53,971	(5,629)
Propane [Member]
Revenues:
Revenues	528,434		485,247		809,483	758,632
Costs and expenses:
Cost of sales	270,777		237,843		408,404	371,871
Other Revenues
Revenues:
Revenues	25,126		25,586		44,971	45,415
Costs and expenses:
Cost of sales	3,504		3,353		7,171	7,034
Ferrellgas, L.P. [Member]
Revenues:
Revenues	553,560		510,833		854,454	804,047
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	115,247		128,233		224,274	242,776
Operating expense - equipment lease expense	6,862		8,261		13,692	16,649
Depreciation and amortization expense	21,249		19,795		42,639	39,014
General and administrative expense	20,254		14,085		33,330	23,781
Non-cash employee stock ownership plan compensation charge	762		630		1,470	1,425
Loss on asset sales and disposals	80		2,148		893	4,383
Operating income	114,825		96,485		122,581	97,114
Interest expense	(46,522)		(38,690)		(93,050)	(75,567)
Other income (expense), net	3,759		76		3,867	(56)
Earnings (loss) before income taxes	72,062		57,871		33,398	21,491
Income tax expense (benefit)	312		115		399	633
Net earnings (loss)	71,750	(38,751)	57,756	(36,898)	32,999	20,858
Other comprehensive income (loss)	28,516	$ 7,917	(2,555)	$ (6,148)	36,433	(8,703)
Comprehensive loss	100,266		55,201		69,432	12,155
Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues	528,434		485,247		809,483	758,632
Costs and expenses:
Cost of sales	270,777		237,843		408,404	371,871
Ferrellgas, L.P. [Member] | Other Revenues
Revenues:
Revenues	25,126		25,586		44,971	45,415
Costs and expenses:
Cost of sales	3,504		3,353		7,171	7,034
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Parent Company [Member]
Revenues:
Revenues	553,560		510,833		854,454	804,047
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	115,247		128,233		224,274	242,776
Operating expense - equipment lease expense	6,862		8,261		13,692	16,649
Depreciation and amortization expense	21,249		19,684		42,639	38,791
General and administrative expense	20,254		14,082		33,328	23,777
Non-cash employee stock ownership plan compensation charge	762		630		1,470	1,425
Loss on asset sales and disposals	80		2,148		893	4,383
Operating income	114,825		96,599		122,583	97,341
Interest expense	(45,958)		(37,778)		(91,859)	(73,469)
Other income (expense), net	3,774		76		3,903	(56)
Earnings (loss) before income taxes	72,641		58,897		34,627	23,816
Income tax expense (benefit)	312		115		399	633
Equity in earnings (loss) of Ferrellgas, L.P.	(1,402)		(194)		(1,110)	(1,658)
Net earnings (loss)	70,927		58,588		33,118	21,525
Other comprehensive income (loss)	28,516		(2,555)		36,433	(8,703)
Comprehensive loss	99,443		56,033		69,551	12,822
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Parent Company [Member] | Propane [Member]
Revenues:
Revenues	528,434		485,247		809,483	758,632
Costs and expenses:
Cost of sales	270,777		237,843		408,404	371,871
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Parent Company [Member] | Other Revenues
Revenues:
Revenues	25,126		25,586		44,971	45,415
Costs and expenses:
Cost of sales	3,504		3,353		7,171	7,034
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Subsidiary Issuer [Member]
Costs and expenses:
General and administrative expense			3		2	4
Operating income			(3)		(2)	(4)
Earnings (loss) before income taxes			(3)		(2)	(4)
Net earnings (loss)			(3)		(2)	(4)
Comprehensive loss			(3)		(2)	(4)
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Costs and expenses:
Other income (expense), net	(15)				(36)
Earnings (loss) before income taxes	(15)				(36)
Net earnings (loss)	(15)				(36)
Comprehensive loss	(15)				(36)
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	2,437		1,050		3,174	1,935
Depreciation and amortization expense			111			223
Operating income	(2,437)		(1,161)		(3,174)	(2,158)
Interest expense	(564)		(912)		(1,191)	(2,098)
Other income (expense), net	1,614		1,882		3,293	2,602
Earnings (loss) before income taxes	(1,387)		(191)		(1,072)	(1,654)
Net earnings (loss)	(1,387)		(191)		(1,072)	(1,654)
Comprehensive loss	(1,387)		(191)		(1,072)	(1,654)
Ferrellgas, L.P. [Member] | Eliminations [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	(2,437)		(1,050)		(3,174)	(1,935)
Operating income	2,437		1,050		3,174	1,935
Other income (expense), net	(1,614)		(1,882)		(3,293)	(2,602)
Earnings (loss) before income taxes	823		(832)		(119)	(667)
Equity in earnings (loss) of Ferrellgas, L.P.	1,402		194		1,110	1,658
Net earnings (loss)	2,225		(638)		991	991
Comprehensive loss	$ 2,225		$ (638)		$ 991	$ 991