Guarantor financial information - Balance Sheets (Details) - USD ($) $ in Thousands	Apr. 30, 2019	Jul. 31, 2018	Apr. 30, 2018	Jul. 31, 2017
Current assets:
Cash and cash equivalents	$ 45,434	$ 119,311	$ 9,499	$ 5,760
Accounts and notes receivable, net	157,229	126,054
Inventories	78,449	83,694
Prepaid expenses and other current assets	25,489	34,862
Total current assets	306,601	363,921
Property, plant and equipment, net	603,923	557,723
Goodwill, net	247,508	246,098
Intangible assets, net	109,634	120,951
Other assets, net	62,326	74,588
Total assets	1,329,992	1,363,281
Current liabilities:
Accounts payable	41,408	46,820
Short-term borrowings	0	32,800
Collateralized note payable	62,000	58,000
Other current liabilities	160,507	142,025
Total current liabilities	263,915	279,645
Long-term debt	2,084,506	2,078,637
Other liabilities	35,879	39,476
Contingencies and commitments
Partners' capital (deficit)
Accumulated other comprehensive income (loss)	(846)	20,510
Total Ferrellgas Partners, L.P. partners' deficit	(1,047,524)	(1,027,785)
Total liabilities and partners' capital (deficit)	1,329,992	1,363,281
Ferrellgas, L.P. [Member]
Current assets:
Cash and cash equivalents	45,365	119,308	9,491	5,701
Accounts and notes receivable, net	157,229	126,054
Inventories	78,449	83,694
Prepaid expenses and other current assets	25,427	34,830
Total current assets	306,470	363,886
Property, plant and equipment, net	603,923	557,723
Goodwill, net	247,508	246,098
Intangible assets, net	109,634	120,951
Other assets, net	62,326	74,588
Total assets	1,329,861	1,363,246
Current liabilities:
Accounts payable	41,408	46,820
Short-term borrowings	0	32,800
Collateralized note payable	62,000	58,000
Other current liabilities	148,875	138,091
Total current liabilities	252,283	275,711
Long-term debt	1,730,874	1,728,137
Other liabilities	35,879	39,476
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	(688,334)	(700,811)
Accumulated other comprehensive income (loss)	(841)	20,733
Total Ferrellgas Partners, L.P. partners' deficit	(689,175)	(680,078)
Total liabilities and partners' capital (deficit)	1,329,861	1,363,246
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Current assets:
Cash and cash equivalents	45,364	119,133	9,126	5,327
Accounts and notes receivable, net	(9,208)	(3,420)
Intercompany Receivables, Current	49,313	15,660
Inventories	78,449	83,694
Prepaid expenses and other current assets	25,427	34,050
Total current assets	189,345	249,117
Property, plant and equipment, net	603,924	557,689
Goodwill, net	247,508	246,098
Intangible assets, net	109,634	120,951
Investment in Ferrellgas, L.P.	52,776	59,937
Other assets, net	58,557	63,411
Total assets	1,261,744	1,297,203
Current liabilities:
Accounts payable	41,296	45,171
Short-term borrowings		32,800
Other current liabilities	142,937	131,702
Total current liabilities	184,233	209,673
Long-term debt	1,730,874	1,728,137
Other liabilities	35,812	39,471
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	(688,334)	(700,811)
Accumulated other comprehensive income (loss)	(841)	20,733
Total Ferrellgas Partners, L.P. partners' deficit	(689,175)	(680,078)
Total liabilities and partners' capital (deficit)	1,261,744	1,297,203
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Subsidiary Issuer [Member]
Current assets:
Cash and cash equivalents	1	1	1	1
Total current assets	1	1
Total assets	1	1
Current liabilities:
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	1	1
Total Ferrellgas Partners, L.P. partners' deficit	1	1
Total liabilities and partners' capital (deficit)	1	1
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents		174	$ 364	$ 373
Accounts and notes receivable, net	150	9,395
Prepaid expenses and other current assets	(1)	775
Total current assets	149	10,344
Property, plant and equipment, net	(1)	34
Other assets, net	2,875	9,961
Total assets	3,023	20,339
Current liabilities:
Accounts payable		1,547
Intercompany Payables	(192)	(143)
Other current liabilities	267	6,036
Total current liabilities	75	7,440
Other liabilities	67	5
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	2,881	12,894
Total Ferrellgas Partners, L.P. partners' deficit	2,881	12,894
Total liabilities and partners' capital (deficit)	3,023	20,339
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Current assets:
Accounts and notes receivable, net	166,287	120,079
Prepaid expenses and other current assets	1	5
Total current assets	166,288	120,084
Other assets, net	894	1,216
Total assets	167,182	121,300
Current liabilities:
Accounts payable	112	102
Collateralized note payable	62,000	58,000
Intercompany Payables	49,505	15,803
Other current liabilities	5,671	353
Total current liabilities	117,288	74,258
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	49,894	47,042
Total Ferrellgas Partners, L.P. partners' deficit	49,894	47,042
Total liabilities and partners' capital (deficit)	167,182	121,300
Eliminations [Member] | Ferrellgas, L.P. [Member]
Current assets:
Intercompany Receivables, Current	(49,313)	(15,660)
Total current assets	(49,313)	(15,660)
Investment in Ferrellgas, L.P.	(52,776)	(59,937)
Total assets	(102,089)	(75,597)
Current liabilities:
Intercompany Payables	(49,313)	(15,660)
Total current liabilities	(49,313)	(15,660)
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	(52,776)	(59,937)
Total Ferrellgas Partners, L.P. partners' deficit	(52,776)	(59,937)
Total liabilities and partners' capital (deficit)	$ (102,089)	$ (75,597)