Guarantor financial information - Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2019	Oct. 31, 2018
Revenues:
Revenues	$ 293,214	$ 352,309
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	114,543	110,331
Depreciation and amortization expense	19,219	18,992
General and administrative expense	9,695	14,179
Operating expense - equipment lease expense	8,388
Equipment lease expense, Topic 840		7,863
Non-cash employee stock ownership plan compensation charge	795	2,748
Loss on asset sales and disposals	2,235	4,504
Operating Income (Loss)	630	(13,491)
Interest expense	(45,697)	(43,878)
Other income (expense), net	(132)	19
Earnings (loss) before income taxes	(45,199)	(57,350)
Income tax expense (benefit)	518	158
Net loss	(45,717)	(57,508)
Other comprehensive loss	(6,148)	(12,587)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(51,865)	(70,095)
Propane [Member]
Revenues:
Revenues	273,385	334,966
Costs and expenses:
Cost of sales	134,028	204,136
Other Revenues
Revenues:
Revenues	19,829	17,343
Costs and expenses:
Cost of sales	3,681	3,047
Ferrellgas, L.P. [Member]
Revenues:
Revenues	293,214	352,309
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	114,543	110,331
Depreciation and amortization expense	19,219	18,992
General and administrative expense	9,696	14,175
Operating expense - equipment lease expense	8,388
Equipment lease expense, Topic 840		7,863
Non-cash employee stock ownership plan compensation charge	795	2,748
Loss on asset sales and disposals	2,235	4,504
Operating Income (Loss)	629	(13,487)
Interest expense	(36,877)	(35,195)
Other income (expense), net	(132)	19
Earnings (loss) before income taxes	(36,380)	(48,663)
Income tax expense (benefit)	518	151
Net loss	(36,898)	(48,814)
Other comprehensive loss	(6,148)	(12,587)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(43,046)	(61,401)
Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues	273,385	334,966
Costs and expenses:
Cost of sales	134,028	204,136
Ferrellgas, L.P. [Member] | Other Revenues
Revenues:
Revenues	19,829	17,343
Costs and expenses:
Cost of sales	3,681	3,047
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues	293,214
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	114,543	110,331
Depreciation and amortization expense	19,107	18,881
General and administrative expense	9,695	14,173
Operating expense - equipment lease expense	8,388
Equipment lease expense, Topic 840		7,863
Non-cash employee stock ownership plan compensation charge	795	2,748
Loss on asset sales and disposals	2,235	1,996
Operating Income (Loss)	742	(10,866)
Interest expense	(35,691)	(34,348)
Other income (expense), net	(132)	19
Earnings (loss) before income taxes	(35,081)	(45,195)
Income tax expense (benefit)	518	151
Equity in earnings (loss) of Ferrellgas, L.P.	(1,464)	(2,282)
Net loss	(37,063)	(47,628)
Other comprehensive loss	(6,148)	(12,587)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(43,211)	(60,215)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Propane [Member]
Revenues:
Revenues	273,385
Costs and expenses:
Cost of sales	134,028
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Other Revenues
Revenues:
Revenues	19,829
Costs and expenses:
Cost of sales	3,681
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Subsidiary Issuer [Member]
Costs and expenses:
General and administrative expense	1	2
Operating Income (Loss)	(1)	(2)
Earnings (loss) before income taxes	(1)	(2)
Net loss	(1)	(2)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1)	(2)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Costs and expenses:
Loss on asset sales and disposals		2,508
Operating Income (Loss)		(2,508)
Earnings (loss) before income taxes		(2,508)
Net loss		(2,508)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		(2,508)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	885	1,017
Depreciation and amortization expense	112	111
Operating Income (Loss)	(997)	(1,128)
Interest expense	(1,186)	(847)
Other income (expense), net	720	2,203
Earnings (loss) before income taxes	(1,463)	228
Net loss	(1,463)	228
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1,463)	228
Eliminations [Member] | Ferrellgas, L.P. [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	(885)	(1,017)
Operating Income (Loss)	885	1,017
Other income (expense), net	(720)	(2,203)
Earnings (loss) before income taxes	165	(1,186)
Equity in earnings (loss) of Ferrellgas, L.P.	1,464	2,282
Net loss	1,629	1,096
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 1,629	1,096
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Other Revenues
Revenues:
Revenues		17,343
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member]
Revenues:
Revenues		352,309
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues		334,966
Costs and expenses:
Cost of sales		204,136
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Other Revenues
Revenues:
Revenues		17,343
Costs and expenses:
Cost of sales		3,047
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues		352,309
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		334,966
Costs and expenses:
Cost of sales		204,136
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		17,343
Costs and expenses:
Cost of sales		$ 3,047