Guarantor financial information - Condensed Consolidated Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Revenues:
Propane and other gas liquids sales	$ 592,239	$ 437,375	$ 894,997	$ 679,774
Midstream operations	117,276	96,787	238,036	204,831
Other	45,641	45,088	76,778	74,187
Total revenues	755,156	579,250	1,209,811	958,792
Costs and expenses:
Cost of product sold - propane and other gas liquids sales	362,918	235,029	542,433	354,241
Cost of sales - midstream operations	107,067	87,024	215,192	181,666
Cost of product sold - other	20,787	20,657	34,489	32,403
Operating expense	123,716	113,076	234,178	218,162
Depreciation and amortization expense	25,485	25,607	51,217	51,809
General and administrative expense	14,891	12,279	28,055	26,548
Equipment lease expense	6,954	7,416	13,695	14,765
Non-cash employee stock ownership plan compensation charge	4,031	2,945	7,993	6,699
Asset Impairment Charges	10,005	0	10,005	0
Loss on disposal of assets	39,249	45	40,144	6,468
Operating income (loss)	40,053	75,172	32,410	66,031
Interest expense	(42,673)	(36,819)	(83,480)	(72,247)
Other income (expense), net	684	763	1,195	1,271
Earnings (loss) before income taxes	(1,936)	39,116	(49,875)	(4,945)
Income tax expense (benefit)	(162)	588	215	(2)
Net earnings (loss)	(1,774)	38,528	(50,090)	(4,943)
Other comprehensive income (loss)	(8,671)	15,776	9,829	25,152
Comprehensive income (loss)	(10,445)	54,304	(40,261)	20,209
Ferrellgas, L.P. [Member]
Revenues:
Propane and other gas liquids sales	592,239	437,375	894,997	679,774
Midstream operations	117,276	96,787	238,036	204,831
Other	45,641	45,088	76,778	74,187
Total revenues	755,156	579,250	1,209,811	958,792
Costs and expenses:
Cost of product sold - propane and other gas liquids sales	362,918	235,029	542,433	354,241
Cost of sales - midstream operations	107,067	87,024	215,192	181,666
Cost of product sold - other	20,787	20,657	34,489	32,403
Operating expense	123,716	113,076	234,178	218,162
Depreciation and amortization expense	25,485	25,607	51,217	51,809
General and administrative expense	14,890	12,278	28,054	26,547
Equipment lease expense	6,954	7,416	13,695	14,765
Non-cash employee stock ownership plan compensation charge	4,031	2,945	7,993	6,699
Asset Impairment Charges	10,005	0	10,005	0
Loss on disposal of assets	39,249	45	40,144	6,468
Operating income (loss)	40,054	75,173	32,411	66,032
Interest expense	(34,058)	(32,748)	(66,254)	(64,146)
Other income (expense), net	684	763	1,195	1,271
Earnings (loss) before income taxes	6,680	43,188	(32,648)	3,157
Income tax expense (benefit)	(167)	588	204	(3)
Equity in earnings of subsidiary	0	0	0	0
Net earnings (loss)	6,847	42,600	(32,852)	3,160
Other comprehensive income (loss)	(8,671)	15,776	9,829	25,152
Comprehensive income (loss)	(1,824)	58,376	(23,023)	28,312
Reportable Legal Entities [Member] | Ferrellgas, L.P. (Parent and Co-Issuer) [Member]
Revenues:
Propane and other gas liquids sales	592,275	437,375	894,392	679,774
Midstream operations	0	0	0	0
Other	22,707	21,609	39,384	38,935
Total revenues	614,982	458,984	933,776	718,709
Costs and expenses:
Cost of product sold - propane and other gas liquids sales	362,927	235,029	541,746	354,241
Cost of sales - midstream operations	0	0	0	0
Cost of product sold - other	2,853	2,571	5,562	5,001
Operating expense	114,096	103,986	215,328	201,641
Depreciation and amortization expense	18,521	18,014	36,868	36,291
General and administrative expense	13,833	11,093	24,588	23,956
Equipment lease expense	6,862	7,267	13,510	14,477
Non-cash employee stock ownership plan compensation charge	4,031	2,945	7,993	6,699
Asset Impairment Charges	0		0
Loss on disposal of assets	555	73	1,463	1,520
Operating income (loss)	91,304	78,006	86,718	74,883
Interest expense	(21,212)	(21,089)	(41,606)	(41,441)
Other income (expense), net	408	304	623	257
Earnings (loss) before income taxes	70,500	57,221	45,735	33,699
Income tax expense (benefit)	82	103	72	74
Equity in earnings of subsidiary	(63,571)	(14,518)	(78,515)	(30,465)
Net earnings (loss)	6,847	42,600	(32,852)	3,160
Other comprehensive income (loss)	(8,671)	15,776	9,829	25,152
Comprehensive income (loss)	(1,824)	58,376	(23,023)	28,312
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Revenues:
Propane and other gas liquids sales	(36)	0	605	0
Midstream operations	117,276	96,787	238,036	204,831
Other	22,934	23,479	37,394	35,252
Total revenues	140,174	120,266	276,035	240,083
Costs and expenses:
Cost of product sold - propane and other gas liquids sales	(9)	0	687	0
Cost of sales - midstream operations	107,067	87,024	215,192	181,666
Cost of product sold - other	17,934	18,086	28,927	27,402
Operating expense	9,795	9,642	19,058	19,888
Depreciation and amortization expense	6,893	7,527	14,206	15,399
General and administrative expense	1,054	1,182	3,461	2,586
Equipment lease expense	92	149	185	288
Non-cash employee stock ownership plan compensation charge	0	0	0	0
Asset Impairment Charges	10,005		10,005
Loss on disposal of assets	38,694	(28)	38,681	4,948
Operating income (loss)	(51,351)	(3,316)	(54,367)	(12,094)
Interest expense	(11,739)	(11,002)	(22,924)	(21,675)
Other income (expense), net	276	459	572	1,014
Earnings (loss) before income taxes	(62,814)	(13,859)	(76,719)	(32,755)
Income tax expense (benefit)	(249)	485	132	(77)
Equity in earnings of subsidiary	0	0	0	0
Net earnings (loss)	(62,565)	(14,344)	(76,851)	(32,678)
Other comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	(62,565)	(14,344)	(76,851)	(32,678)
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Revenues:
Propane and other gas liquids sales	0	0	0	0
Midstream operations	0	0	0	0
Other	0	0	0	0
Total revenues	0	0	0	0
Costs and expenses:
Cost of product sold - propane and other gas liquids sales	0	0	0	0
Cost of sales - midstream operations	0	0	0	0
Cost of product sold - other	0	0	0	0
Operating expense	1,833	539	3,015	(1,566)
Depreciation and amortization expense	71	66	143	119
General and administrative expense	0	0	0	0
Equipment lease expense	0	0	0	0
Non-cash employee stock ownership plan compensation charge	0	0	0	0
Asset Impairment Charges	0		0
Loss on disposal of assets	0	0	0	0
Operating income (loss)	(1,904)	(605)	(3,158)	1,447
Interest expense	(1,107)	(657)	(1,724)	(1,027)
Other income (expense), net	2,008	1,091	3,223	1,798
Earnings (loss) before income taxes	(1,003)	(171)	(1,659)	2,218
Income tax expense (benefit)	0	0	0	0
Equity in earnings of subsidiary	0	0	0	0
Net earnings (loss)	(1,003)	(171)	(1,659)	2,218
Other comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	(1,003)	(171)	(1,659)	2,218
Reportable Legal Entities [Member] | Ferrellgas Finance Corp. (Co-Issuer) [Member]
Revenues:
Propane and other gas liquids sales	0	0	0	0
Midstream operations	0	0	0	0
Other	0	0	0	0
Total revenues	0	0	0	0
Costs and expenses:
Cost of product sold - propane and other gas liquids sales	0	0	0	0
Cost of sales - midstream operations	0	0	0	0
Cost of product sold - other	0	0	0	0
Operating expense	0	0	0	0
Depreciation and amortization expense	0	0	0	0
General and administrative expense	3	3	5	5
Equipment lease expense	0	0	0	0
Non-cash employee stock ownership plan compensation charge	0	0	0	0
Asset Impairment Charges	0		0
Loss on disposal of assets	0	0	0	0
Operating income (loss)	(3)	(3)	(5)	(5)
Interest expense	0	0	0	0
Other income (expense), net	0	0	0	0
Earnings (loss) before income taxes	(3)	(3)	(5)	(5)
Income tax expense (benefit)	0	0	0	0
Equity in earnings of subsidiary	0	0	0	0
Net earnings (loss)	(3)	(3)	(5)	(5)
Other comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	(3)	(3)	(5)	(5)
Eliminations [Member]
Revenues:
Propane and other gas liquids sales	0	0	0	0
Midstream operations	0	0	0	0
Other	0	0	0	0
Total revenues	0	0	0	0
Costs and expenses:
Cost of product sold - propane and other gas liquids sales	0	0	0	0
Cost of sales - midstream operations	0	0	0	0
Cost of product sold - other	0	0	0	0
Operating expense	(2,008)	(1,091)	(3,223)	(1,801)
Depreciation and amortization expense	0	0	0	0
General and administrative expense	0	0	0	0
Equipment lease expense	0	0	0	0
Non-cash employee stock ownership plan compensation charge	0	0	0	0
Asset Impairment Charges	0		0
Loss on disposal of assets	0	0	0	0
Operating income (loss)	2,008	1,091	3,223	1,801
Interest expense	0	0	0	(3)
Other income (expense), net	(2,008)	(1,091)	(3,223)	(1,798)
Earnings (loss) before income taxes	0	0	0	0
Income tax expense (benefit)	0	0	0	0
Equity in earnings of subsidiary	63,571	14,518	78,515	30,465
Net earnings (loss)	63,571	14,518	78,515	30,465
Other comprehensive income (loss)	0	0	0	0
Comprehensive income (loss)	$ 63,571	$ 14,518	$ 78,515	$ 30,465