Guarantor financial information - Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Revenues:
Revenues	$ 573,377	$ 755,156	$ 925,686	$ 1,209,811
Costs and expenses:
Operating expense	121,219	123,716	231,550	234,178
Depreciation and amortization expense	19,605	25,485	38,597	51,217
General and administrative expense	16,342	14,891	30,521	28,055
Equipment lease expense	8,415	6,954	16,278	13,695
Non-cash employee stock ownership plan compensation charge	1,944	4,031	4,692	7,993
Asset impairment charges		10,005	0	10,005
Loss on asset sales and disposals	2,216	39,249	6,720	40,144
Operating Income (Loss)	88,683	40,053	75,192	32,410
Interest expense	(44,891)	(42,673)	(88,769)	(83,480)
Other income (expense), net	86	684	105	1,195
Earnings (loss) before income taxes	43,878	(1,936)	(13,472)	(49,875)
Income tax expense (benefit)	3	(162)	161	215
Net earnings (loss)	43,875	(1,774)	(13,633)	(50,090)
Other comprehensive income (loss)	(17,273)	(8,671)	(29,860)	9,829
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	26,602	(10,445)	(43,493)	(40,261)
Propane [Member]
Revenues:
Revenues	550,112	592,239	885,078	894,997
Costs and expenses:
Cost of sales	311,531	362,918	515,667	542,433
Midstream Operations [Member]
Revenues:
Revenues	0	117,276	0	238,036
Costs and expenses:
Cost of sales	0	107,067	0	215,192
Product and Service, Other [Member]
Revenues:
Revenues	23,265	45,641	40,608	76,778
Costs and expenses:
Cost of sales	3,422	20,787	6,469	34,489
Ferrellgas, L.P. [Member]
Revenues:
Revenues	573,377	755,156	925,686	1,209,811
Costs and expenses:
Operating expense	121,219	123,716	231,550	234,178
Depreciation and amortization expense	19,605	25,485	38,597	51,217
General and administrative expense	16,341	14,890	30,516	28,054
Equipment lease expense	8,415	6,954	16,278	13,695
Non-cash employee stock ownership plan compensation charge	1,944	4,031	4,692	7,993
Asset impairment charges		10,005	0	10,005
Loss on asset sales and disposals	2,216	39,249	6,720	40,144
Operating Income (Loss)	88,684	40,054	75,197	32,411
Interest expense	(36,150)	(34,058)	(71,345)	(66,254)
Other income (expense), net	86	684	105	1,195
Earnings (loss) before income taxes	52,620	6,680	3,957	(32,648)
Income tax expense (benefit)	3	(167)	154	204
Net earnings (loss)	52,617	6,847	3,803	(32,852)
Other comprehensive income (loss)	(17,273)	(8,671)	(29,860)	9,829
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	35,344	(1,824)	(26,057)	(23,023)
Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues	550,112	592,239	885,078	894,997
Costs and expenses:
Cost of sales	311,531	362,918	515,667	542,433
Ferrellgas, L.P. [Member] | Midstream Operations [Member]
Revenues:
Revenues	0	117,276	0	238,036
Costs and expenses:
Cost of sales	0	107,067	0	215,192
Ferrellgas, L.P. [Member] | Product and Service, Other [Member]
Revenues:
Revenues	23,265	45,641	40,608	76,778
Costs and expenses:
Cost of sales	3,422	20,787	6,469	34,489
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues	573,328		925,637
Costs and expenses:
Operating expense	121,180	114,096	231,511	215,328
Depreciation and amortization expense	19,493	18,521	38,374	36,868
General and administrative expense	16,338	13,833	30,511	24,588
Equipment lease expense	8,415	6,862	16,278	13,510
Non-cash employee stock ownership plan compensation charge	1,944	4,031	4,692	7,993
Loss on asset sales and disposals	2,045	555	4,041	1,463
Operating Income (Loss)	89,074	91,304	78,208	86,718
Interest expense	(34,655)	(21,212)	(69,003)	(41,606)
Other income (expense), net	96	408	115	623
Earnings (loss) before income taxes	54,515	70,500	9,320	45,735
Income tax expense (benefit)	3	82	154	72
Equity in earnings (loss) of Ferrellgas, L.P.	(863)	(63,571)	(3,145)	(78,515)
Net earnings (loss)	53,649	6,847	6,021	(32,852)
Other comprehensive income (loss)	(17,273)	(8,671)	(29,860)	9,829
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	36,376	(1,824)	(23,839)	(23,023)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Propane [Member]
Revenues:
Revenues	550,112		885,078
Costs and expenses:
Cost of sales	311,531		515,667
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member] | Product and Service, Other [Member]
Revenues:
Revenues	23,216		40,559
Costs and expenses:
Cost of sales	3,308		6,355
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Subsidiary Issuer [Member]
Costs and expenses:
General and administrative expense	3	3	5	5
Operating Income (Loss)	(3)	(3)	(5)	(5)
Earnings (loss) before income taxes	(3)	(3)	(5)	(5)
Net earnings (loss)	(3)	(3)	(5)	(5)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(3)	(3)	(5)	(5)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Revenues:
Revenues	49		49
Costs and expenses:
Operating expense	39	9,795	39	19,058
Depreciation and amortization expense		6,893		14,206
General and administrative expense		1,054		3,461
Equipment lease expense		92		185
Asset impairment charges		10,005		10,005
Loss on asset sales and disposals	171	38,694	2,679	38,681
Operating Income (Loss)	(275)	(51,351)	(2,783)	(54,367)
Interest expense	(38)	(11,739)	(38)	(22,924)
Other income (expense), net	(10)	276	(10)	572
Earnings (loss) before income taxes	(323)	(62,814)	(2,831)	(76,719)
Income tax expense (benefit)		(249)		132
Net earnings (loss)	(323)	(62,565)	(2,831)	(76,851)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(323)	(62,565)	(2,831)	(76,851)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member] | Product and Service, Other [Member]
Revenues:
Revenues	49		49
Costs and expenses:
Cost of sales	114		114
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Costs and expenses:
Operating expense	1,884	1,833	2,901	3,015
Depreciation and amortization expense	112	71	223	143
Operating Income (Loss)	(1,996)	(1,904)	(3,124)	(3,158)
Interest expense	(1,457)	(1,107)	(2,304)	(1,724)
Other income (expense), net	2,916	2,008	5,119	3,223
Earnings (loss) before income taxes	(537)	(1,003)	(309)	(1,659)
Net earnings (loss)	(537)	(1,003)	(309)	(1,659)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(537)	(1,003)	(309)	(1,659)
Eliminations [Member] | Ferrellgas, L.P. [Member]
Costs and expenses:
Operating expense	(1,884)	(2,008)	(2,901)	(3,223)
Operating Income (Loss)	1,884	2,008	2,901	3,223
Other income (expense), net	(2,916)	(2,008)	(5,119)	(3,223)
Earnings (loss) before income taxes	(1,032)		(2,218)
Equity in earnings (loss) of Ferrellgas, L.P.	863	63,571	3,145	78,515
Net earnings (loss)	(169)	63,571	927	78,515
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ (169)	63,571	$ 927	78,515
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Product and Service, Other [Member]
Revenues:
Revenues		45,641		76,778
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member]
Revenues:
Revenues		755,156		1,209,811
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Propane [Member]
Revenues:
Revenues		592,239		894,997
Costs and expenses:
Cost of sales		362,918		542,433
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Midstream Operations [Member]
Revenues:
Revenues		117,276		238,036
Costs and expenses:
Cost of sales		107,067		215,192
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Ferrellgas, L.P. [Member] | Product and Service, Other [Member]
Revenues:
Revenues		45,641		76,778
Costs and expenses:
Cost of sales		20,787		34,489
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Revenues:
Revenues		614,982		933,776
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		592,275		894,392
Costs and expenses:
Cost of sales		362,927		541,746
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		22,707		39,384
Costs and expenses:
Cost of sales		2,853		5,562
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Revenues:
Revenues		140,174		276,035
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		(36)		605
Costs and expenses:
Cost of sales		(9)		687
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		117,276		238,036
Costs and expenses:
Cost of sales		107,067		215,192
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		22,934		37,394
Costs and expenses:
Cost of sales		$ 17,934		$ 28,927