Guarantor financial information - Balance Sheets (Details) - USD ($) $ in Thousands	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Current assets:
Cash and cash equivalents	$ 333,761	$ 11,054	$ 119,311	$ 5,760
Accounts and notes receivable, net	101,438	107,596
Inventories	72,664	80,454
Prepaid expenses and other current assets	35,944	42,275
Total current assets	543,807	241,379
Property, plant and equipment, net	591,042	596,723
Goodwill, net	247,195	247,195
Intangible assets, net	104,049	108,557
Operating lease, right-of-use assets	107,349
Other assets, net	74,748	69,105
Total assets	1,668,190	1,262,959
Current liabilities:
Accounts payable	33,944	33,364
Short-term borrowings	0	43,000
Collateralized note payable		62,000
Current portion of long-term debt	859,095	631,756
Current operating lease liabilities	29,345
Other current liabilities	167,466	138,237
Total current liabilities	1,089,850	908,357
Long-term debt	1,646,396	1,457,004
Operating lease liabilities	89,022
Other liabilities	51,190	36,536
Contingencies and commitments	0	0
Partners' capital (deficit)
Accumulated other comprehensive income (loss)	(2,303)	(14,512)
Total Ferrellgas Partners, L.P. partners' deficit	(1,200,042)	(1,131,233)
Total liabilities and partners' capital (deficit)	1,668,190	1,262,959
Parent Company [Member]
Current assets:
Cash and cash equivalents	6	8	3	59
Prepaid expenses and other current assets	22	57
Total assets	28	65
Current liabilities:
Current portion of long-term debt	357,000	354,727
Other current liabilities	19,305	3,873
Partners' capital (deficit)
Accumulated other comprehensive income (loss)	(2,303)	(14,512)
Total Ferrellgas Partners, L.P. partners' deficit	(1,200,042)	(1,131,233)
Total liabilities and partners' capital (deficit)	28	65
Reportable Legal Entities [Member] | Parent Company [Member]
Current assets:
Cash and cash equivalents	332,244	11,045	119,133	5,327
Accounts and notes receivable, net	11,879	(3,912)
Intercompany Receivables, Current	69,980	(5,650)
Inventories	72,664	80,454
Prepaid expenses and other current assets	35,897	42,158
Total current assets	522,664	124,095
Property, plant and equipment, net	591,042	596,724
Goodwill, net	247,195	247,195
Intangible assets, net	104,049	108,557
Investment in Ferrellgas, L.P.	37,662	52,999
Operating lease, right-of-use assets	107,349
Other assets, net	72,137	65,447
Total assets	1,682,098	1,195,017
Current liabilities:
Accounts payable	33,944	33,252
Short-term borrowings		43,000
Collateralized note payable		0
Intercompany Payables	0	0
Current portion of long-term debt	502,095	277,029
Current operating lease liabilities	29,345
Other current liabilities	162,097	128,666
Total current liabilities	727,481	481,947
Long-term debt	1,646,396	1,457,004
Operating lease liabilities	89,022
Other liabilities	51,190	36,469
Partners' capital (deficit)
Partners' equity	(829,678)	(765,756)
Accumulated other comprehensive income (loss)	(2,313)	(14,647)
Total Ferrellgas Partners, L.P. partners' deficit	(831,991)	(780,403)
Total liabilities and partners' capital (deficit)	1,682,098	1,195,017
Reportable Legal Entities [Member] | Subsidiary Issuer [Member]
Current assets:
Cash and cash equivalents	1	1	1	1
Accounts and notes receivable, net	0	0
Intercompany Receivables, Current	0	0
Inventories	0	0
Prepaid expenses and other current assets	0	0
Total current assets	1	1
Property, plant and equipment, net	0	0
Goodwill, net	0	0
Intangible assets, net	0	0
Investment in Ferrellgas, L.P.	0	0
Other assets, net	0	0
Total assets	1	1
Current liabilities:
Accounts payable	0	0
Short-term borrowings		0
Collateralized note payable		0
Intercompany Payables	0	0
Other current liabilities	0	0
Total current liabilities	0	0
Long-term debt	0	0
Other liabilities	0	0
Partners' capital (deficit)
Partners' equity	1	1
Accumulated other comprehensive income (loss)	0	0
Total Ferrellgas Partners, L.P. partners' deficit	1	1
Total liabilities and partners' capital (deficit)	1	1
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	0	0	174	373
Accounts and notes receivable, net	24	35
Intercompany Receivables, Current	0	0
Inventories	0	0
Prepaid expenses and other current assets	0	(1)
Total current assets	24	34
Property, plant and equipment, net	0	(1)
Goodwill, net	0	0
Intangible assets, net	0	0
Investment in Ferrellgas, L.P.	0	0
Other assets, net	2,255	2,875
Total assets	2,279	2,908
Current liabilities:
Accounts payable	0	0
Short-term borrowings		0
Collateralized note payable		0
Intercompany Payables	0	(192)
Other current liabilities	0	20
Total current liabilities	0	(172)
Long-term debt	0	0
Other liabilities	0	67
Partners' capital (deficit)
Partners' equity	2,279	3,013
Accumulated other comprehensive income (loss)	0	0
Total Ferrellgas Partners, L.P. partners' deficit	2,279	3,013
Total liabilities and partners' capital (deficit)	2,279	2,908
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	1,510	0	0	0
Accounts and notes receivable, net	89,535	111,473
Intercompany Receivables, Current	0	0
Inventories	0	0
Prepaid expenses and other current assets	0	0
Total current assets	91,045	111,473
Property, plant and equipment, net	0	0
Goodwill, net	0	0
Intangible assets, net	0	0
Investment in Ferrellgas, L.P.	0	0
Other assets, net	356	783
Total assets	91,401	112,256
Current liabilities:
Accounts payable	0	112
Short-term borrowings		0
Collateralized note payable		62,000
Intercompany Payables	69,980	(5,458)
Other current liabilities	(13,961)	5,617
Total current liabilities	56,019	62,271
Long-term debt	0	0
Other liabilities	0	0
Partners' capital (deficit)
Partners' equity	35,382	49,985
Accumulated other comprehensive income (loss)	0	0
Total Ferrellgas Partners, L.P. partners' deficit	35,382	49,985
Total liabilities and partners' capital (deficit)	91,401	112,256
Eliminations [Member]
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts and notes receivable, net	0	0
Intercompany Receivables, Current	(69,980)	5,650
Inventories	0	0
Prepaid expenses and other current assets	0	0
Total current assets	(69,980)	5,650
Property, plant and equipment, net	0	0
Goodwill, net	0	0
Intangible assets, net	0	0
Investment in Ferrellgas, L.P.	(37,662)	(52,999)
Other assets, net	0	0
Total assets	(107,642)	(47,349)
Current liabilities:
Accounts payable	0	0
Short-term borrowings		0
Collateralized note payable		0
Intercompany Payables	(69,980)	5,650
Other current liabilities	0	0
Total current liabilities	(69,980)	5,650
Long-term debt	0	0
Other liabilities	0	0
Partners' capital (deficit)
Partners' equity	(37,662)	(52,999)
Accumulated other comprehensive income (loss)	0	0
Total Ferrellgas Partners, L.P. partners' deficit	(37,662)	(52,999)
Total liabilities and partners' capital (deficit)	(107,642)	(47,349)
Ferrellgas, L.P. [Member]
Current assets:
Cash and cash equivalents	333,755	11,046	$ 119,308	$ 5,701
Accounts and notes receivable, net	101,438	107,596
Intercompany Receivables, Current	0	0
Inventories	72,664	80,454
Prepaid expenses and other current assets	35,897	42,157
Total current assets	543,754	241,253
Property, plant and equipment, net	591,042	596,723
Goodwill, net	247,195	247,195
Intangible assets, net	104,049	108,557
Investment in Ferrellgas, L.P.	0	0
Operating lease, right-of-use assets	107,349
Other assets, net	74,748	69,105
Total assets	1,668,137	1,262,833
Current liabilities:
Accounts payable	33,944	33,364
Short-term borrowings	0	43,000
Collateralized note payable		62,000
Intercompany Payables	0	0
Current portion of long-term debt	502,095	277,029
Current operating lease liabilities	29,345
Other current liabilities	148,136	134,303
Total current liabilities	713,520	549,696
Long-term debt	1,646,396	1,457,004
Operating lease liabilities	89,022
Other liabilities	51,190	36,536
Contingencies and commitments	0	0
Partners' capital (deficit)
Partners' equity	(829,678)	(765,756)
Accumulated other comprehensive income (loss)	(2,313)	(14,647)
Total Ferrellgas Partners, L.P. partners' deficit	(831,991)	(780,403)
Total liabilities and partners' capital (deficit)	$ 1,668,137	$ 1,262,833