Guarantor financial information - Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 7,111	$ (17,614)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(6,400)	(4,625)
Capital expenditures	(18,126)	(23,433)
Proceeds from sale of assets	835	1,061
Cash payments to construct assets in connection with future lease transactions	(16,879)
Cash receipts in connection with leased vehicles	5,863
Other		(292)
Net cash used in investing activities	(34,707)	(27,289)
Cash flows from financing activities:
Distributions		(9,814)
Payments on long-term debt	(512)	(281)
Net additions to (reductions in) short-term borrowings	37,000	(32,800)
Net additions to collateralized short-term borrowings	11,000	32,000
Cash paid for financing costs and other	(1,140)	(224)
Net cash used in financing activities	46,347	(11,220)
Increase (decrease) in cash and cash equivalents	18,751	(56,123)
Cash and cash equivalents	29,805	63,188	$ 11,054	$ 119,311
Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	7,147	(17,606)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(6,400)	(4,625)
Capital expenditures	(18,126)	(23,433)
Proceeds from sale of assets	835	1,061
Cash payments to construct assets in connection with future lease transactions	(16,879)
Cash receipts in connection with leased vehicles	5,863
Other		(292)
Net cash used in investing activities	(34,707)	(27,289)
Cash flows from financing activities:
Distributions	(101)	(10,015)
Payments on long-term debt	(512)	(281)
Net additions to (reductions in) short-term borrowings	37,000	(32,800)
Net additions to collateralized short-term borrowings	11,000	32,000
Cash paid for financing costs and other	(1,140)	(224)
Net cash used in financing activities	46,247	(11,320)
Increase (decrease) in cash and cash equivalents	18,687	(56,215)
Cash and cash equivalents	29,733	63,093	11,046	119,308
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	21,350	11,666
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(6,400)	(4,625)
Capital expenditures	(18,126)	(23,433)
Proceeds from sale of assets	835	1,061
Cash payments to construct assets in connection with future lease transactions	(16,879)
Cash receipts in connection with leased vehicles	5,863
Net changes in advances with consolidated entities		2,585
Intercompany loan to affiliate	(3,203)
Other		(292)
Net cash used in investing activities	(37,910)	(24,704)
Cash flows from financing activities:
Distributions	(101)	(10,015)
Payments on long-term debt	(512)	(281)
Net additions to (reductions in) short-term borrowings	37,000	(32,800)
Cash paid for financing costs and other	(1,140)	(213)
Net cash used in financing activities	35,247	(43,309)
Increase (decrease) in cash and cash equivalents	18,687	(56,347)
Cash and cash equivalents	29,732	62,786	11,045	119,133
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Subsidiary Issuer [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(1)	(2)
Cash flows from financing activities:
Net changes in advances with consolidated entities	1	2
Net cash used in financing activities	1	2
Cash and cash equivalents	1	1	$ 1	1
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	506	19,961
Cash flows from financing activities:
Net changes in advances with consolidated entities	(506)	(19,829)
Net cash used in financing activities	(506)	(19,829)
Increase (decrease) in cash and cash equivalents		132
Cash and cash equivalents		306		$ 174
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(3,708)	(17,231)
Cash flows from investing activities:
Cash collected from securitization of accounts receivable	161,600	242,912
Cash remitted for accounts receivable	(172,600)	(274,912)
Net cash used in investing activities	(11,000)	(32,000)
Cash flows from financing activities:
Net additions to collateralized short-term borrowings	11,000	32,000
Net changes in advances with consolidated entities	3,708	17,242
Cash paid for financing costs and other		(11)
Net cash used in financing activities	14,708	49,231
Eliminations [Member] | Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(11,000)	(32,000)
Cash flows from investing activities:
Cash collected from securitization of accounts receivable	(161,600)	(242,912)
Cash remitted for accounts receivable	172,600	274,912
Net changes in advances with consolidated entities		(2,585)
Intercompany loan to affiliate	3,203
Net cash used in investing activities	14,203	29,415
Cash flows from financing activities:
Net changes in advances with consolidated entities	(3,203)	2,585
Net cash used in financing activities	$ (3,203)	$ 2,585