Guarantor financial information - Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Apr. 30, 2019	Apr. 30, 2018
Revenues:
Revenues	$ 479,625			$ 515,810			$ 1,405,311	$ 1,725,621
Costs and expenses:
Operating expense	119,991			116,579			351,541	350,757
Depreciation and amortization expense	20,617			25,348			59,214	76,565
General and administrative expense	11,516			11,678			42,037	39,733
Equipment lease expense	8,319			7,133			24,597	20,828
DQC NEVER NEGATIVE Non-cash employee stock ownership plan compensation charge	(4)			2,738			4,688	10,731
Asset impairment charges								10,005
Loss on asset sales and disposals	1,683			6,270			8,403	46,414
Operating Income (Loss)	64,794			51,277			139,986	83,687
Interest expense	(44,162)			(40,375)			(132,931)	(123,855)
Other income (expense), net	251			227			356	1,422
Earnings (loss) before income taxes	20,883			11,129			7,411	(38,746)
Income tax expense (benefit)	123			67			284	282
Net earnings (loss)	20,760	$ 43,875	$ (57,508)	11,062	$ (1,774)	$ (48,316)	7,127	(39,028)
Other comprehensive income (loss)	8,286	(17,273)	(12,587)	(6,727)	(8,671)	18,500	(21,574)	3,102
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	29,046			4,335			(14,447)	(35,926)
Propane [Member]
Revenues:
Revenues	459,556			451,302			1,344,634	1,346,299
Costs and expenses:
Cost of sales	250,389			260,419			766,056	802,852
Midstream Operations [Member]
Revenues:
Revenues				22,595				260,631
Costs and expenses:
Cost of sales				14,518				229,710
Product and Service, Other [Member]
Revenues:
Revenues	20,069			41,913			60,677	118,691
Costs and expenses:
Cost of sales	2,320			19,850			8,789	54,339
Ferrellgas, L.P. [Member]
Revenues:
Revenues	479,625			515,810			1,405,311	1,725,621
Costs and expenses:
Operating expense	119,991			116,579			351,541	350,757
Depreciation and amortization expense	20,617			25,348			59,214	76,565
General and administrative expense	11,512			11,546			42,028	39,600
Equipment lease expense	8,319			7,133			24,597	20,828
DQC NEVER NEGATIVE Non-cash employee stock ownership plan compensation charge	(4)			2,738			4,688	10,731
Asset impairment charges								10,005
Loss on asset sales and disposals	1,683			6,270			8,403	46,414
Operating Income (Loss)	64,798			51,409			139,995	83,820
Interest expense	(35,395)			(31,739)			(106,740)	(97,993)
Other income (expense), net	251			227			356	1,422
Earnings (loss) before income taxes	29,654			19,897			33,611	(12,751)
Income tax expense (benefit)	100			57			254	261
Net earnings (loss)	29,554	52,617	(48,814)	19,840	6,847	(39,699)	33,357	(13,012)
Other comprehensive income (loss)	8,286	$ (17,273)	$ (12,587)	(6,727)	$ (8,671)	$ 18,500	(21,574)	3,102
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	37,840			13,113			11,783	(9,910)
Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues	459,556			451,302			1,344,634	1,346,299
Costs and expenses:
Cost of sales	250,389			260,419			766,056	802,852
Ferrellgas, L.P. [Member] | Midstream Operations [Member]
Revenues:
Revenues				22,595				260,631
Costs and expenses:
Cost of sales				14,518				229,710
Ferrellgas, L.P. [Member] | Product and Service, Other [Member]
Revenues:
Revenues	20,069			41,913			60,677	118,691
Costs and expenses:
Cost of sales	2,320			19,850			8,789	54,339
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues	479,625						1,405,262
Costs and expenses:
Operating expense	124,078			108,291			355,589	323,619
Depreciation and amortization expense	20,506			19,105			58,880	55,973
General and administrative expense	11,511			10,460			42,022	35,048
Equipment lease expense	8,319			7,045			24,597	20,555
DQC NEVER NEGATIVE Non-cash employee stock ownership plan compensation charge	(4)			2,738			4,688	10,731
Loss on asset sales and disposals	1,683			2,243			5,724	3,706
Operating Income (Loss)	60,823			58,386			139,031	145,104
Interest expense	(34,206)			(20,297)			(103,209)	(61,903)
Other income (expense), net	278			(133)			393	490
Earnings (loss) before income taxes	26,895			37,956			36,215	83,691
Income tax expense (benefit)	(49)			102			105	174
Equity in earnings (loss) of Ferrellgas, L.P.	392			(18,014)			(2,753)	(96,529)
Net earnings (loss)	27,336			19,840			33,357	(13,012)
Other comprehensive income (loss)	8,286			(6,727)			(21,574)	3,102
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	35,622			13,113			11,783	(9,910)
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
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Product and Service, Other [Member]
Revenues:
Revenues	20,069						60,628
Costs and expenses:
Cost of sales	2,320						8,675
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Subsidiary Issuer [Member]
Costs and expenses:
General and administrative expense	1						6	5
Operating Income (Loss)	(1)						(6)	(5)
Earnings (loss) before income taxes	(1)						(6)	(5)
Net earnings (loss)	(1)						(6)	(5)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1)						(6)	(5)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Revenues:
Revenues							49
Costs and expenses:
Operating expense	(3)			9,262			36	28,320
Depreciation and amortization expense				6,171				20,377
General and administrative expense				1,086				4,547
Equipment lease expense				88				273
Asset impairment charges								10,005
Loss on asset sales and disposals				4,027			2,679	42,708
Operating Income (Loss)	3			(7,879)			(2,780)	(62,246)
Interest expense				(10,104)			(38)	(33,028)
Other income (expense), net	(27)			360			(37)	932
Earnings (loss) before income taxes	(24)			(17,623)			(2,855)	(94,342)
Income tax expense (benefit)	149			(45)			149	87
Net earnings (loss)	(173)			(17,578)			(3,004)	(94,429)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(173)			(17,578)			(3,004)	(94,429)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member] | Product and Service, Other [Member]
Revenues:
Revenues							49
Costs and expenses:
Cost of sales							114
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Costs and expenses:
Operating expense	968			1,459			3,869	4,474
Depreciation and amortization expense	111			72			334	215
Operating Income (Loss)	(1,079)			(1,531)			(4,203)	(4,689)
Interest expense	(1,189)			(1,338)			(3,493)	(3,062)
Other income (expense), net	2,834			2,433			7,953	5,656
Earnings (loss) before income taxes	566			(436)			257	(2,095)
Net earnings (loss)	566			(436)			257	(2,095)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	566			(436)			257	(2,095)
Eliminations [Member] | Ferrellgas, L.P. [Member]
Costs and expenses:
Operating expense	(5,052)			(2,433)			(7,953)	(5,656)
Operating Income (Loss)	5,052			2,433			7,953	5,656
Other income (expense), net	(2,834)			(2,433)			(7,953)	(5,656)
Earnings (loss) before income taxes	2,218
Equity in earnings (loss) of Ferrellgas, L.P.	(392)			18,014			2,753	96,529
Net earnings (loss)	1,826			18,014			2,753	96,529
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 1,826			18,014			$ 2,753	96,529
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Product and Service, Other [Member]
Revenues:
Revenues				41,913				118,691
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member]
Revenues:
Revenues				515,810				1,725,621
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues				451,302				1,346,299
Costs and expenses:
Cost of sales				260,419				802,852
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Midstream Operations [Member]
Revenues:
Revenues				22,595				260,631
Costs and expenses:
Cost of sales				14,518				229,710
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Product and Service, Other [Member]
Revenues:
Revenues				41,913				118,691
Costs and expenses:
Cost of sales				19,850				54,339
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues				470,913				1,404,689
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				451,212				1,345,604
Costs and expenses:
Cost of sales				260,317				802,063
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Product and Service, Other [Member]
Revenues:
Revenues				19,701				59,085
Costs and expenses:
Cost of sales				2,328				7,890
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Revenues:
Revenues				44,897				320,932
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member] | Propane [Member]
Revenues:
Revenues				90				695
Costs and expenses:
Cost of sales				102				789
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member] | Midstream Operations [Member]
Revenues:
Revenues				22,595				260,631
Costs and expenses:
Cost of sales				14,518				229,710
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member] | Product and Service, Other [Member]
Revenues:
Revenues				22,212				59,606
Costs and expenses:
Cost of sales				$ 17,522				$ 46,449