Guarantor financial information - Balance Sheets (Details) - USD ($) $ in Thousands	Apr. 30, 2020	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2018
Current assets:
Cash and cash equivalents	$ 318,847	$ 11,054	$ 45,434	$ 119,311
Accounts and notes receivable, net	142,952	107,596
Inventories	65,209	80,454
Prepaid expenses and other current assets	47,223	42,275
Total current assets	574,231	241,379
Property, plant and equipment, net	596,978	596,723
Goodwill, net	247,195	247,195
Intangible assets, net	103,966	108,557
Operating lease, right-of-use assets	110,497
Other assets, net	87,472	69,105
Total assets	1,720,339	1,262,959
Current liabilities:
Accounts payable	37,025	33,364
Short-term borrowings	0	43,000
Collateralized note payable		62,000
Current portion of long-term debt	359,050	631,756
Current operating lease liabilities	31,914
Other current liabilities	174,823	138,237
Total current liabilities	602,812	908,357
Long-term debt	2,146,044	1,457,004
Operating lease liabilities	76,133
Other liabilities	52,167	36,536
Contingencies and commitments
Partners' capital (deficit)
Accumulated other comprehensive income (loss)	(20,580)	(14,512)
Total Ferrellgas Partners, L.P. partners' deficit	(1,149,032)	(1,131,233)
Total liabilities and partners' capital (deficit)	1,720,339	1,262,959
Ferrellgas, L.P. [Member]
Current assets:
Cash and cash equivalents	318,837	11,046	45,365	119,308
Accounts and notes receivable, net	142,952	107,596
Inventories	65,209	80,454
Prepaid expenses and other current assets	47,175	42,157
Total current assets	574,173	241,253
Property, plant and equipment, net	596,978	596,723
Goodwill, net	247,195	247,195
Intangible assets, net	103,966	108,557
Operating lease, right-of-use assets	110,497
Other assets, net	87,472	69,105
Total assets	1,720,281	1,262,833
Current liabilities:
Accounts payable	37,025	33,364
Short-term borrowings	0	43,000
Collateralized note payable		62,000
Current portion of long-term debt	2,050	277,029
Current operating lease liabilities	31,914
Other current liabilities	163,191	134,303
Total current liabilities	234,180	549,696
Long-term debt	2,146,044	1,457,004
Operating lease liabilities	76,133
Other liabilities	52,167	36,536
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	(767,465)	(765,756)
Accumulated other comprehensive income (loss)	(20,778)	(14,647)
Total Ferrellgas Partners, L.P. partners' deficit	(788,243)	(780,403)
Total liabilities and partners' capital (deficit)	1,720,281	1,262,833
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Current assets:
Cash and cash equivalents	318,836	11,045	45,364	119,133
Accounts and notes receivable, net	10,642	(3,912)
Intercompany Receivables, Current	99,362	(5,650)
Inventories	65,209	80,454
Prepaid expenses and other current assets	47,175	42,158
Total current assets	541,224	124,095
Property, plant and equipment, net	596,978	596,724
Goodwill, net	247,195	247,195
Intangible assets, net	103,966	108,557
Investment in Ferrellgas, L.P.	37,505	52,999
Operating lease, right-of-use assets	110,497
Other assets, net	84,772	65,447
Total assets	1,722,137	1,195,017
Current liabilities:
Accounts payable	37,025	33,252
Short-term borrowings		43,000
Current portion of long-term debt	2,050	277,029
Current operating lease liabilities	31,914
Other current liabilities	165,047	128,666
Total current liabilities	236,036	481,947
Long-term debt	2,146,044	1,457,004
Operating lease liabilities	76,133
Other liabilities	52,167	36,469
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	(767,465)	(765,756)
Accumulated other comprehensive income (loss)	(20,778)	(14,647)
Total Ferrellgas Partners, L.P. partners' deficit	(788,243)	(780,403)
Total liabilities and partners' capital (deficit)	1,722,137	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				$ 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	12	20
Total current liabilities	12	(172)
Other liabilities		67
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	2,267	3,013
Total Ferrellgas Partners, L.P. partners' deficit	2,267	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	132,286	111,473
Total current assets	132,286	111,473
Other assets, net	445	783
Total assets	132,731	112,256
Current liabilities:
Accounts payable		112
Collateralized note payable		62,000
Intercompany Payables	99,362	(5,458)
Other current liabilities	(1,868)	5,617
Total current liabilities	97,494	62,271
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	35,237	49,985
Total Ferrellgas Partners, L.P. partners' deficit	35,237	49,985
Total liabilities and partners' capital (deficit)	132,731	112,256
Eliminations [Member] | Ferrellgas, L.P. [Member]
Current assets:
Intercompany Receivables, Current	(99,362)	5,650
Total current assets	(99,362)	5,650
Investment in Ferrellgas, L.P.	(37,505)	(52,999)
Total assets	(136,867)	(47,349)
Current liabilities:
Intercompany Payables	(99,362)	5,650
Total current liabilities	(99,362)	5,650
Contingencies and commitments
Partners' capital (deficit)
Partners' equity	(37,505)	(52,999)
Total Ferrellgas Partners, L.P. partners' deficit	(37,505)	(52,999)
Total liabilities and partners' capital (deficit)	$ (136,867)	$ (47,349)