Guarantor financial information - Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2020	Oct. 31, 2019
Revenues:
Revenues	$ 300,894	$ 293,214
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	109,027	114,543
Operating expense - equipment lease expense	6,830	8,388
Depreciation and amortization expense	21,390	19,219
General and administrative expense	13,080	9,695
Non-cash employee stock ownership plan compensation charge	708	795
Loss on asset sales and disposals	813	2,235
Operating income	7,752	630
Interest expense	(54,226)	(45,697)
Other income (expense), net	108	(132)
Loss before income taxes	(46,366)	(45,199)
Income tax expense (benefit)	87	518
Net loss	(46,453)	(45,717)
Other comprehensive income (loss)	7,917	(6,148)
Comprehensive loss	(38,536)	(51,865)
Propane [Member]
Revenues:
Revenues	281,049	273,385
Costs and expenses:
Cost of sales	137,627	134,028
Other Revenues
Revenues:
Revenues	19,845	19,829
Costs and expenses:
Cost of sales	3,667	3,681
Ferrellgas, L.P. [Member]
Revenues:
Revenues	300,894	293,214
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	109,027	114,543
Operating expense - equipment lease expense	6,830	8,388
Depreciation and amortization expense	21,390	19,219
General and administrative expense	13,076	9,696
Non-cash employee stock ownership plan compensation charge	708	795
Loss on asset sales and disposals	813	2,235
Operating income	7,756	629
Interest expense	(46,528)	(36,877)
Other income (expense), net	108	(132)
Loss before income taxes	(38,664)	(36,380)
Income tax expense (benefit)	87	518
Net loss	(38,751)	(36,898)
Other comprehensive income (loss)	7,917	(6,148)
Comprehensive loss	(30,834)	(43,046)
Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues	281,049	273,385
Costs and expenses:
Cost of sales	137,627	134,028
Ferrellgas, L.P. [Member] | Other Revenues
Revenues:
Revenues	19,845	19,829
Costs and expenses:
Cost of sales	3,667	3,681
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Parent Company [Member]
Revenues:
Revenues	300,894	293,214
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	109,027	114,543
Operating expense - equipment lease expense	6,830	8,388
Depreciation and amortization expense	21,390	19,107
General and administrative expense	13,074	9,695
Non-cash employee stock ownership plan compensation charge	708	795
Loss on asset sales and disposals	813	2,235
Operating income	7,758	742
Interest expense	(45,901)	(35,691)
Other income (expense), net	129	(132)
Loss before income taxes	(38,014)	(35,081)
Income tax expense (benefit)	87	518
Equity in earnings (loss) of Ferrellgas, L.P.	292	(1,464)
Net loss	(37,809)	(37,063)
Other comprehensive income (loss)	7,917	(6,148)
Comprehensive loss	(29,892)	(43,211)
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Parent Company [Member] | Propane [Member]
Revenues:
Revenues	281,049	273,385
Costs and expenses:
Cost of sales	137,627	134,028
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Parent Company [Member] | Other Revenues
Revenues:
Revenues	19,845	19,829
Costs and expenses:
Cost of sales	3,667	3,681
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Subsidiary Issuer [Member]
Costs and expenses:
General and administrative expense	2	1
Operating income	(2)	(1)
Loss before income taxes	(2)	(1)
Net loss	(2)	(1)
Comprehensive loss	(2)	(1)
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Costs and expenses:
Other income (expense), net	(21)
Loss before income taxes	(21)
Net loss	(21)
Comprehensive loss	(21)
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	737	885
Depreciation and amortization expense		112
Operating income	(737)	(997)
Interest expense	(627)	(1,186)
Other income (expense), net	1,679	720
Loss before income taxes	315	(1,463)
Net loss	315	(1,463)
Comprehensive loss	315	(1,463)
Ferrellgas, L.P. [Member] | Eliminations [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	(737)	(885)
Operating income	737	885
Other income (expense), net	(1,679)	(720)
Loss before income taxes	(942)	165
Equity in earnings (loss) of Ferrellgas, L.P.	(292)	1,464
Net loss	(1,234)	1,629
Comprehensive loss	$ (1,234)	$ 1,629