Guarantor financial information - Balance Sheets (Details) - USD ($) $ in Thousands	Jan. 31, 2019	Jul. 31, 2018	Jan. 31, 2018	Jul. 31, 2017
Current assets:
Cash and cash equivalents	$ 40,647	$ 119,311	$ 14,173	$ 5,760
Accounts and notes receivable, net	203,164	126,054
Inventories	89,784	83,694
Prepaid expenses and other current assets	36,616	34,862
Total current assets	370,211	363,921
Property, plant and equipment, net	584,334	557,723
Goodwill, net	247,478	246,098
Intangible assets, net	113,558	120,951
Other assets, net	72,539	74,588
Total assets	1,388,120	1,363,281
Current liabilities:
Accounts payable	63,639	46,820
Short-term borrowings	0	32,800
Collateralized note payable	140,000	58,000
Other current liabilities	147,253	142,025
Total current liabilities	350,892	279,645
Long-term debt	2,083,031	2,078,637
Other liabilities	37,547	39,476
Contingencies and commitments
Partners' capital (deficit)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	(1,083,350)	(1,034,477)
Accumulated other comprehensive income (loss)	(9,049)	20,510
Total liabilities and partners' capital (deficit)	1,388,120	1,363,281
Total Ferrellgas Partners, L.P. partners' deficit	(1,076,184)	(1,027,785)
Ferrellgas, L.P. [Member]
Current assets:
Cash and cash equivalents	40,552	119,308	14,171	5,701
Accounts and notes receivable, net	203,164	126,054
Inventories	89,784	83,694
Prepaid expenses and other current assets	36,553	34,830
Total current assets	370,053	363,886
Property, plant and equipment, net	584,334	557,723
Goodwill, net	247,478	246,098
Intangible assets, net	113,558	120,951
Other assets, net	72,539	74,588
Total assets	1,387,962	1,363,246
Current liabilities:
Accounts payable	63,639	46,820
Short-term borrowings	0	32,800
Collateralized note payable	140,000	58,000
Other current liabilities	143,319	138,091
Total current liabilities	346,958	275,711
Long-term debt	1,730,468	1,728,137
Other liabilities	37,547	39,476
Contingencies and commitments
Partners' capital (deficit)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	(727,011)	(680,078)
Accumulated other comprehensive income (loss)	(9,127)	20,733
Total liabilities and partners' capital (deficit)	1,387,962	1,363,246
Total Ferrellgas Partners, L.P. partners' deficit	(717,884)	(700,811)
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Current assets:
Cash and cash equivalents	40,305	119,133	13,954	5,327
Accounts and notes receivable, net	(3,661)	(3,420)
Intercompany Receivables, Current	(9,201)	15,660
Inventories	89,784	83,694
Prepaid expenses and other current assets	36,551	34,050
Total current assets	153,778	249,117
Property, plant and equipment, net	584,335	557,689
Goodwill, net	247,478	246,098
Intangible assets, net	113,558	120,951
Investment in Ferrellgas, L.P.	74,072	59,937
Other assets, net	68,659	63,411
Total assets	1,241,880	1,297,203
Current liabilities:
Accounts payable	63,526	45,171
Short-term borrowings		32,800
Other current liabilities	137,417	131,702
Total current liabilities	200,943	209,673
Long-term debt	1,730,468	1,728,137
Other liabilities	37,480	39,471
Contingencies and commitments
Partners' capital (deficit)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	(727,011)	(680,078)
Accumulated other comprehensive income (loss)	(9,127)	20,733
Total liabilities and partners' capital (deficit)	1,241,880	1,297,203
Total Ferrellgas Partners, L.P. partners' deficit	(717,884)	(700,811)
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' Capital, Including Portion Attributable to Noncontrolling Interest	1	1
Total liabilities and partners' capital (deficit)	1	1
Total Ferrellgas Partners, L.P. partners' deficit	1	1
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	246	174	$ 216	$ 373
Accounts and notes receivable, net	150	9,395
Prepaid expenses and other current assets	(1)	775
Total current assets	395	10,344
Property, plant and equipment, net	(1)	34
Other assets, net	2,875	9,961
Total assets	3,269	20,339
Current liabilities:
Accounts payable		1,547
Intercompany Payables	(192)	(143)
Other current liabilities	388	6,036
Total current liabilities	196	7,440
Other liabilities	67	5
Contingencies and commitments
Partners' capital (deficit)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	3,006	12,894
Total liabilities and partners' capital (deficit)	3,269	20,339
Total Ferrellgas Partners, L.P. partners' deficit	3,006	12,894
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Current assets:
Accounts and notes receivable, net	206,675	120,079
Prepaid expenses and other current assets	3	5
Total current assets	206,678	120,084
Other assets, net	1,005	1,216
Total assets	207,683	121,300
Current liabilities:
Accounts payable	113	102
Collateralized note payable	140,000	58,000
Intercompany Payables	(9,009)	15,803
Other current liabilities	5,514	353
Total current liabilities	136,618	74,258
Contingencies and commitments
Partners' capital (deficit)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	71,065	47,042
Total liabilities and partners' capital (deficit)	207,683	121,300
Total Ferrellgas Partners, L.P. partners' deficit	71,065	47,042
Eliminations [Member] | Ferrellgas, L.P. [Member]
Current assets:
Intercompany Receivables, Current	9,201	(15,660)
Total current assets	9,201	(15,660)
Investment in Ferrellgas, L.P.	(74,072)	(59,937)
Total assets	(64,871)	(75,597)
Current liabilities:
Intercompany Payables	9,201	(15,660)
Total current liabilities	9,201	(15,660)
Contingencies and commitments
Partners' capital (deficit)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	(74,072)	(59,937)
Total liabilities and partners' capital (deficit)	(64,871)	(75,597)
Total Ferrellgas Partners, L.P. partners' deficit	$ (74,072)	$ (59,937)