Guarantor financial information - Balance Sheets (Details) - USD ($) $ in Thousands	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Current assets:
Cash and cash equivalents	$ 11,054	$ 119,311	$ 5,760	$ 4,965
Accounts and notes receivable, net	107,596	126,054
Inventories	80,454	83,694
Prepaid expenses and other current assets	42,275	34,862
Total current assets	241,379	363,921
Property, plant and equipment, net	596,723	557,723
Goodwill, net	247,195	246,098
Intangible assets, net	108,557	120,951
Other assets, net	69,105	74,588
Total assets	1,262,959	1,363,281
Current liabilities:
Accounts payable	33,364	46,820
Short-term borrowings	43,000	32,800
Collateralized note payable	62,000	58,000
Current portion of long-term debt	631,756	2,402
Other current liabilities	138,237	139,623
Total current liabilities	908,357	279,645
Long-term debt	1,457,004	2,078,637
Other liabilities	36,536	39,476
Contingencies and commitments	0	0
Partners' capital (deficit)
Accumulated other comprehensive income (loss)	(14,512)	20,510
Total Ferrellgas Partners, L.P. partners' deficit	(1,131,233)	(1,027,785)
Total liabilities and partners' capital (deficit)	1,262,959	1,363,281
Parent Company [Member]
Current assets:
Cash and cash equivalents	8	3	59	75
Prepaid expenses and other current assets	57	23
Total assets	65	26
Current liabilities:
Current portion of long-term debt	354,727
Other current liabilities	3,873	3,925
Long-term debt		350,500
Partners' capital (deficit)
Accumulated other comprehensive income (loss)	(14,512)	20,510
Total Ferrellgas Partners, L.P. partners' deficit	(1,131,233)	(1,027,785)
Total liabilities and partners' capital (deficit)	65	26
Ferrellgas, L.P. [Member]
Current assets:
Cash and cash equivalents	11,046	119,308	5,701	4,890
Accounts and notes receivable, net	107,596	126,054
Intercompany Receivables, Current	0	0
Inventories	80,454	83,694
Prepaid expenses and other current assets	42,157	34,830
Total current assets	241,253	363,886
Property, plant and equipment, net	596,723	557,723
Goodwill, net	247,195	246,098
Intangible assets, net	108,557	120,951
Investment in Ferrellgas, L.P.	0	0
Other assets, net	69,105	74,588
Total assets	1,262,833	1,363,246
Current liabilities:
Accounts payable	33,364	46,820
Short-term borrowings	43,000	32,800
Collateralized note payable	62,000	58,000
Intercompany Payables	0	0
Current portion of long-term debt	277,029	2,402
Other current liabilities	134,303	135,689
Total current liabilities	549,696	275,711
Long-term debt	1,457,004	1,728,137
Other liabilities	36,536	39,476
Contingencies and commitments	0	0
Partners' capital (deficit)
Partners' equity	(765,756)	(700,811)
Accumulated other comprehensive income (loss)	(14,647)	20,733
Total Ferrellgas Partners, L.P. partners' deficit	(780,403)	(680,078)
Total liabilities and partners' capital (deficit)	1,262,833	1,363,246
Reportable Legal Entities [Member] | Parent Company [Member]
Current assets:
Cash and cash equivalents	11,045	119,133	5,327	4,472
Accounts and notes receivable, net	(3,912)	(3,420)
Intercompany Receivables, Current	(5,650)	15,660
Inventories	80,454	83,694
Prepaid expenses and other current assets	42,158	34,050
Total current assets	124,095	249,117
Property, plant and equipment, net	596,724	557,689
Goodwill, net	247,195	246,098
Intangible assets, net	108,557	120,951
Investment in Ferrellgas, L.P.	52,999	59,937
Other assets, net	65,447	63,411
Total assets	1,195,017	1,297,203
Current liabilities:
Accounts payable	33,252	45,171
Short-term borrowings	43,000	32,800
Collateralized note payable	0	0
Intercompany Payables	0	0
Current portion of long-term debt	277,029	2,402
Other current liabilities	128,666	129,300
Total current liabilities	481,947	209,673
Long-term debt	1,457,004	1,728,137
Other liabilities	36,469	39,471
Partners' capital (deficit)
Partners' equity	(765,756)	(700,811)
Accumulated other comprehensive income (loss)	(14,647)	20,733
Total Ferrellgas Partners, L.P. partners' deficit	(780,403)	(680,078)
Total liabilities and partners' capital (deficit)	1,195,017	1,297,203
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	0
Collateralized note payable	0	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	174	373	417
Accounts and notes receivable, net	35	9,395
Intercompany Receivables, Current	0	0
Inventories	0	0
Prepaid expenses and other current assets	(1)	775
Total current assets	34	10,344
Property, plant and equipment, net	(1)	34
Goodwill, net	0	0
Intangible assets, net	0	0
Investment in Ferrellgas, L.P.	0	0
Other assets, net	2,875	9,961
Total assets	2,908	20,339
Current liabilities:
Accounts payable	0	1,547
Short-term borrowings	0	0
Collateralized note payable	0	0
Intercompany Payables	(192)	(143)
Other current liabilities	20	6,036
Total current liabilities	(172)	7,440
Long-term debt	0	0
Other liabilities	67	5
Partners' capital (deficit)
Partners' equity	3,013	12,894
Accumulated other comprehensive income (loss)	0	0
Total Ferrellgas Partners, L.P. partners' deficit	3,013	12,894
Total liabilities and partners' capital (deficit)	2,908	20,339
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts and notes receivable, net	111,473	120,079
Intercompany Receivables, Current	0	0
Inventories	0	0
Prepaid expenses and other current assets	0	5
Total current assets	111,473	120,084
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	783	1,216
Total assets	112,256	121,300
Current liabilities:
Accounts payable	112	102
Short-term borrowings	0	0
Collateralized note payable	62,000	58,000
Intercompany Payables	(5,458)	15,803
Other current liabilities	5,617	353
Total current liabilities	62,271	74,258
Long-term debt	0	0
Other liabilities	0	0
Partners' capital (deficit)
Partners' equity	49,985	47,042
Accumulated other comprehensive income (loss)	0	0
Total Ferrellgas Partners, L.P. partners' deficit	49,985	47,042
Total liabilities and partners' capital (deficit)	112,256	121,300
Eliminations [Member]
Current assets:
Cash and cash equivalents	0	0	$ 0	$ 0
Accounts and notes receivable, net	0	0
Intercompany Receivables, Current	5,650	(15,660)
Inventories	0	0
Prepaid expenses and other current assets	0	0
Total current assets	5,650	(15,660)
Property, plant and equipment, net	0	0
Goodwill, net	0	0
Intangible assets, net	0	0
Investment in Ferrellgas, L.P.	(52,999)	(59,937)
Other assets, net	0	0
Total assets	(47,349)	(75,597)
Current liabilities:
Accounts payable	0	0
Short-term borrowings	0	0
Collateralized note payable	0	0
Intercompany Payables	5,650	(15,660)
Other current liabilities	0	0
Total current liabilities	5,650	(15,660)
Long-term debt	0	0
Other liabilities	0	0
Partners' capital (deficit)
Partners' equity	(52,999)	(59,937)
Accumulated other comprehensive income (loss)	0	0
Total Ferrellgas Partners, L.P. partners' deficit	(52,999)	(59,937)
Total liabilities and partners' capital (deficit)	$ (47,349)	$ (75,597)