Guarantor financial information - Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Apr. 30, 2020	Apr. 30, 2019
Revenues:
Revenues	$ 412,130			$ 479,625			$ 1,216,177	$ 1,405,311
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	121,558			119,991			364,334	351,541
Depreciation and amortization expense	20,366			20,617			59,380	59,214
General and administrative expense	12,560			11,516			36,447	42,037
Operating expense - equipment lease expense	8,075						24,724
Equipment lease expense, preadoption				8,319				24,597
Non-cash employee stock ownership plan compensation charge	757			(4)			2,182	4,688
Loss on extinguishment of debt	37,399						37,399
Loss on asset sales and disposals	1,859			1,683			6,242	8,403
Operating Income (Loss)	67,950			64,794			164,958	139,986
Interest expense	(45,703)			(44,162)			(138,948)	(132,931)
Other income (expense), net	(158)			251			(214)	356
Earnings (loss) before income taxes	(15,310)			20,883			(11,603)	7,411
Income tax expense (benefit)	161			123			794	284
Net earnings (loss)	(15,471)	$ 48,791	$ (45,717)	20,760	$ 43,875	$ (57,508)	(12,397)	7,127
Other comprehensive income (loss)	2,572	(2,555)	(6,148)	8,286	(17,273)	(12,587)	(6,131)	(21,574)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(12,899)			29,046			(18,528)	(14,447)
Propane [Member]
Revenues:
Revenues	391,745			459,556			1,150,377	1,344,634
Costs and expenses:
Cost of sales	176,265			250,389			548,136	766,056
Other Revenues
Revenues:
Revenues	20,385			20,069			65,800	60,677
Costs and expenses:
Cost of sales	2,740			2,320			9,774	8,789
Ferrellgas, L.P. [Member]
Revenues:
Revenues	412,130			479,625			1,216,177	1,405,311
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	121,558			119,991			364,334	351,541
Depreciation and amortization expense	20,366			20,617			59,380	59,214
General and administrative expense	12,555			11,512			36,336	42,028
Operating expense - equipment lease expense	8,075						24,724
Equipment lease expense, preadoption				8,319				24,597
Non-cash employee stock ownership plan compensation charge	757			(4)			2,182	4,688
Loss on extinguishment of debt	37,399						37,399
Loss on asset sales and disposals	1,859			1,683			6,242	8,403
Operating Income (Loss)	67,955			64,798			165,069	139,995
Interest expense	(38,006)			(35,395)			(113,573)	(106,740)
Other income (expense), net	(158)			251			(214)	356
Earnings (loss) before income taxes	(7,608)			29,654			13,883	33,611
Income tax expense (benefit)	112			100			745	254
Net earnings (loss)	(7,720)	57,756	(36,898)	29,554	52,617	(48,814)	13,138	33,357
Other comprehensive income (loss)	2,572	$ (2,555)	$ (6,148)	8,286	$ (17,273)	$ (12,587)	(6,131)	(21,574)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(5,148)			37,840			7,007	11,783
Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues	391,745			459,556			1,150,377	1,344,634
Costs and expenses:
Cost of sales	176,265			250,389			548,136	766,056
Ferrellgas, L.P. [Member] | Other Revenues
Revenues:
Revenues	20,385			20,069			65,800	60,677
Costs and expenses:
Cost of sales	2,740			2,320			9,774	8,789
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues	412,130						1,216,177
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	121,558			124,078			364,334	355,589
Depreciation and amortization expense	20,252			20,506			59,043	58,880
General and administrative expense	12,555			11,511			36,332	42,022
Operating expense - equipment lease expense	8,075						24,724
Equipment lease expense, preadoption				8,319				24,597
Non-cash employee stock ownership plan compensation charge	757			(4)			2,182	4,688
Loss on extinguishment of debt	37,399						37,399
Loss on asset sales and disposals	1,859			1,683			6,242	5,724
Operating Income (Loss)	68,069			60,823			165,410	139,031
Interest expense	(36,943)			(34,206)			(110,412)	(103,209)
Other income (expense), net	(158)			278			(214)	393
Earnings (loss) before income taxes	(6,431)			26,895			17,385	36,215
Income tax expense (benefit)	112			(49)			745	105
Equity in earnings (loss) of Ferrellgas, L.P.	(1,140)			392			(2,798)	(2,753)
Net earnings (loss)	(7,683)			27,336			13,842	33,357
Other comprehensive income (loss)	2,572			8,286			(6,131)	(21,574)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(5,111)			35,622			7,711	11,783
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Propane [Member]
Revenues:
Revenues	391,745						1,150,377
Costs and expenses:
Cost of sales	176,265						548,136
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Other Revenues
Revenues:
Revenues	20,385						65,800
Costs and expenses:
Cost of sales	2,740						9,774
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Subsidiary Issuer [Member]
Costs and expenses:
General and administrative expense				1			4	6
Operating Income (Loss)				(1)			(4)	(6)
Earnings (loss) before income taxes				(1)			(4)	(6)
Net earnings (loss)				(1)			(4)	(6)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest				(1)			(4)	(6)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other				(3)				36
Loss on asset sales and disposals								2,679
Operating Income (Loss)				3				(2,780)
Interest expense								(38)
Other income (expense), net				(27)				(37)
Earnings (loss) before income taxes				(24)				(2,855)
Income tax expense (benefit)				149				149
Net earnings (loss)				(173)				(3,004)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest				(173)				(3,004)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	1,314			968				3,869
Depreciation and amortization expense	114			111			337	334
Operating expense - equipment lease expense							3,249
Operating Income (Loss)	(1,428)			(1,079)			(3,586)	(4,203)
Interest expense	(1,063)			(1,189)			(3,161)	(3,493)
Other income (expense), net	1,351			2,834			3,953	7,953
Earnings (loss) before income taxes	(1,140)			566			(2,794)	257
Net earnings (loss)	(1,140)			566			(2,794)	257
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1,140)			566			(2,794)	257
Eliminations [Member] | Ferrellgas, L.P. [Member]
Costs and expenses:
Operating expense - personnel, vehicle, plant and other	(1,314)			(5,052)				(7,953)
Operating expense - equipment lease expense							(3,249)
Operating Income (Loss)	1,314			5,052			3,249	7,953
Other income (expense), net	(1,351)			(2,834)			(3,953)	(7,953)
Earnings (loss) before income taxes	(37)			2,218			(704)
Equity in earnings (loss) of Ferrellgas, L.P.	1,140			(392)			2,798	2,753
Net earnings (loss)	1,103			1,826			2,094	2,753
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 1,103			1,826			$ 2,094	2,753
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Other Revenues
Revenues:
Revenues				20,069				60,677
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member]
Revenues:
Revenues				479,625				1,405,311
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues				459,556				1,344,634
Costs and expenses:
Cost of sales				250,389				766,056
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Other Revenues
Revenues:
Revenues				20,069				60,677
Costs and expenses:
Cost of sales				2,320				8,789
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues				479,625				1,405,262
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				459,556				1,344,634
Costs and expenses:
Cost of sales				250,389				766,056
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				20,069				60,628
Costs and expenses:
Cost of sales				$ 2,320				8,675
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Revenues:
Revenues								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
Costs and expenses:
Cost of sales								$ 114