Guarantor financial information - Balance Sheets (Details) - USD ($) $ in Thousands	Jan. 31, 2020	Jul. 31, 2019	Jan. 31, 2019	Jul. 31, 2018
Current assets:
Cash and cash equivalents	$ 13,706	$ 11,054	$ 40,647	$ 119,311
Accounts and notes receivable, net	182,444	107,596
Inventories	78,474	80,454
Prepaid expenses and other current assets	47,751	42,275
Total current assets	322,375	241,379
Property, plant and equipment, net	594,007	596,723
Goodwill, net	247,195	247,195
Intangible assets, net	106,214	108,557
Operating lease, right-of-use assets	120,423
Other assets, net	80,998	69,105
Total assets	1,471,212	1,262,959
Current liabilities:
Accounts payable	46,125	33,364
Short-term borrowings	40,000	43,000
Collateralized note payable	121,000	62,000
Current portion of long-term debt	359,157	631,756
Current operating lease liabilities	33,263
Other current liabilities	155,340	138,237
Total current liabilities	754,885	908,357
Long-term debt	1,731,197	1,457,004
Operating lease liabilities	84,546
Other liabilities	45,259	36,536
Contingencies and commitments
Partners' capital (deficit)
Accumulated other comprehensive income (loss)	(23,126)	(14,512)
Total Ferrellgas Partners, L.P. partners' deficit	(1,136,934)	(1,131,233)
Total liabilities and partners' capital (deficit)	1,471,212	1,262,959
Ferrellgas, L.P. [Member]
Current assets:
Cash and cash equivalents	13,643	11,046	40,552	119,308
Accounts and notes receivable, net	182,444	107,596
Inventories	78,474	80,454
Prepaid expenses and other current assets	47,703	42,157
Total current assets	322,264	241,253
Property, plant and equipment, net	594,007	596,723
Goodwill, net	247,195	247,195
Intangible assets, net	106,214	108,557
Operating lease, right-of-use assets	120,423
Other assets, net	80,998	69,105
Total assets	1,471,101	1,262,833
Current liabilities:
Accounts payable	46,125	33,364
Short-term borrowings	40,000	43,000
Collateralized note payable	121,000	62,000
Current portion of long-term debt	2,157	277,029
Current operating lease liabilities	33,263
Other current liabilities	151,406	134,303
Total current liabilities	393,951	549,696
Long-term debt	1,731,197	1,457,004
Operating lease liabilities	84,546
Other liabilities	45,259	36,536
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	(760,502)	(765,756)
Accumulated other comprehensive income (loss)	(23,350)	(14,647)
Total Ferrellgas Partners, L.P. partners' deficit	(783,852)	(780,403)
Total liabilities and partners' capital (deficit)	1,471,101	1,262,833
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Current assets:
Cash and cash equivalents	13,642	11,045	40,305	119,133
Accounts and notes receivable, net	9,646	(3,912)
Intercompany Receivables, Current	(12,388)	(5,650)
Inventories	78,474	80,454
Prepaid expenses and other current assets	47,703	42,158
Total current assets	137,077	124,095
Property, plant and equipment, net	594,007	596,724
Goodwill, net	247,195	247,195
Intangible assets, net	106,214	108,557
Investment in Ferrellgas, L.P.	69,194	52,999
Operating lease, right-of-use assets	120,423
Other assets, net	78,184	65,447
Total assets	1,352,294	1,195,017
Current liabilities:
Accounts payable	46,125	33,252
Short-term borrowings	40,000	43,000
Current portion of long-term debt	2,157	277,029
Current operating lease liabilities	33,263
Other current liabilities	153,599	128,666
Total current liabilities	275,144	481,947
Long-term debt	1,731,197	1,457,004
Operating lease liabilities	84,546
Other liabilities	45,259	36,469
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	(760,502)	(765,756)
Accumulated other comprehensive income (loss)	(23,350)	(14,647)
Total Ferrellgas Partners, L.P. partners' deficit	(783,852)	(780,403)
Total liabilities and partners' capital (deficit)	1,352,294	1,195,017
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			$ 246	$ 174
Accounts and notes receivable, net	24	35
Prepaid expenses and other current assets		(1)
Total current assets	24	34
Property, plant and equipment, net		(1)
Other assets, net	2,255	2,875
Total assets	2,279	2,908
Current liabilities:
Intercompany Payables		(192)
Other current liabilities	13	20
Total current liabilities	13	(172)
Other liabilities		67
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	2,266	3,013
Total Ferrellgas Partners, L.P. partners' deficit	2,266	3,013
Total liabilities and partners' capital (deficit)	2,279	2,908
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Current assets:
Accounts and notes receivable, net	172,774	111,473
Total current assets	172,774	111,473
Other assets, net	559	783
Total assets	173,333	112,256
Current liabilities:
Accounts payable		112
Collateralized note payable	121,000	62,000
Intercompany Payables	(12,388)	(5,458)
Other current liabilities	(2,206)	5,617
Total current liabilities	106,406	62,271
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	66,927	49,985
Total Ferrellgas Partners, L.P. partners' deficit	66,927	49,985
Total liabilities and partners' capital (deficit)	173,333	112,256
Eliminations [Member] | Ferrellgas, L.P. [Member]
Current assets:
Intercompany Receivables, Current	12,388	5,650
Total current assets	12,388	5,650
Investment in Ferrellgas, L.P.	(69,194)	(52,999)
Total assets	(56,806)	(47,349)
Current liabilities:
Intercompany Payables	12,388	5,650
Total current liabilities	12,388	5,650
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	(69,194)	(52,999)
Total Ferrellgas Partners, L.P. partners' deficit	(69,194)	(52,999)
Total liabilities and partners' capital (deficit)	$ (56,806)	$ (47,349)