Guarantor financial information - Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Apr. 30, 2018	Apr. 30, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	$ 78,311	$ 118,331
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(14,862)	(3,539)
Capital expenditures	(58,961)	(35,412)
Proceeds from sale of assets	57,802	4,721
Other	0	(37)
Net cash used in investing activities	(16,021)	(34,267)
Cash flows from financing activities:
Distributions	(29,440)	(69,920)
Proceeds from increase in long-term debt	23,580	220,354
Payments on long-term debt	(1,892)	(173,471)
Net additions to (reductions in) short-term borrowings	(84,179)	(62,902)
Net additions to collateralized short-term borrowings	35,000	27,000
Cash paid for financing costs	(1,161)	(5,633)
Net cash used in financing activities	(58,551)	(79,523)
Increase (decrease) in cash and cash equivalents	3,739	4,541
Cash and cash equivalents - beginning of period	5,760	4,965
Cash and cash equivalents - end of period	9,499	9,506
Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	93,946	124,399
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(14,862)	(3,539)
Capital expenditures	(58,961)	(35,412)
Proceeds from sale of assets	57,802	4,721
Cash collected for purchase of interest in accounts receivable	0	0
Cash remitted to Ferrellgas, L.P for accounts receivable	0	0
Intercompany loan to affiliate	0	0
Other	0	(37)
Net cash used in investing activities	(16,021)	(34,267)
Cash flows from financing activities:
Distributions	(45,495)	(94,413)
Contributions from partners	0	167,640
Proceeds from increase in long-term debt	23,580	52,354
Payments on long-term debt	(1,892)	(173,471)
Net additions to (reductions in) short-term borrowings	(84,179)	(62,902)
Net additions to collateralized short-term borrowings	35,000	27,000
Net changes in advances with consolidated entities	0	0
Cash paid for financing costs	(1,149)	(2,064)
Net cash used in financing activities	(74,135)	(85,856)
Increase (decrease) in cash and cash equivalents	3,790	4,276
Cash and cash equivalents - beginning of period	5,701	4,890
Cash and cash equivalents - end of period	9,491	9,166
Reportable Legal Entities [Member] | Ferrellgas, L.P. (Parent and Co-Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	65,604	186,530
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(14,862)	(3,539)
Capital expenditures	(57,158)	(35,116)
Proceeds from sale of assets	2,479	4,721
Cash collected for purchase of interest in accounts receivable	0	0
Cash remitted to Ferrellgas, L.P for accounts receivable	0	0
Intercompany loan to affiliate	116,871	(35,476)
Other		(37)
Net cash used in investing activities	47,330	(69,447)
Cash flows from financing activities:
Distributions	(45,495)	(94,413)
Contributions from partners		167,640
Proceeds from increase in long-term debt	23,580	52,354
Payments on long-term debt	(1,892)	(173,471)
Net additions to (reductions in) short-term borrowings	(84,179)	(62,902)
Net additions to collateralized short-term borrowings	0	0
Net changes in advances with consolidated entities	0	0
Cash paid for financing costs	(1,149)	(1,820)
Net cash used in financing activities	(109,135)	(112,612)
Increase (decrease) in cash and cash equivalents	3,799	4,471
Cash and cash equivalents - beginning of period	5,327	4,472
Cash and cash equivalents - end of period	9,126	8,943
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	(3,531)	(73,168)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0	0
Capital expenditures	(1,803)	(296)
Proceeds from sale of assets	55,323	0
Cash collected for purchase of interest in accounts receivable	0	0
Cash remitted to Ferrellgas, L.P for accounts receivable	0	0
Intercompany loan to affiliate	0	0
Other		0
Net cash used in investing activities	53,520	(296)
Cash flows from financing activities:
Distributions	0	0
Contributions from partners		0
Proceeds from increase in long-term debt	0	0
Payments on long-term debt	0	0
Net additions to (reductions in) short-term borrowings	0	0
Net additions to collateralized short-term borrowings	0	0
Net changes in advances with consolidated entities	(49,998)	73,269
Cash paid for financing costs	0	0
Net cash used in financing activities	(49,998)	73,269
Increase (decrease) in cash and cash equivalents	(9)	(195)
Cash and cash equivalents - beginning of period	373	417
Cash and cash equivalents - end of period	364	222
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	66,878	38,042
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0	0
Capital expenditures	0	0
Proceeds from sale of assets	0	0
Cash collected for purchase of interest in accounts receivable	985,084	803,109
Cash remitted to Ferrellgas, L.P for accounts receivable	(1,020,084)	(830,109)
Intercompany loan to affiliate	0	244
Other		0
Net cash used in investing activities	(35,000)	(26,756)
Cash flows from financing activities:
Distributions	0	0
Contributions from partners		0
Proceeds from increase in long-term debt	0	0
Payments on long-term debt	0	0
Net additions to (reductions in) short-term borrowings	0	0
Net additions to collateralized short-term borrowings	35,000	27,000
Net changes in advances with consolidated entities	(66,878)	(38,042)
Cash paid for financing costs	0	(244)
Net cash used in financing activities	(31,878)	(11,286)
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents - beginning of period	0	0
Cash and cash equivalents - end of period	0	0
Reportable Legal Entities [Member] | Ferrellgas Finance Corp. (Co-Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	(5)	(5)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0	0
Capital expenditures	0	0
Proceeds from sale of assets	0	0
Cash collected for purchase of interest in accounts receivable	0	0
Cash remitted to Ferrellgas, L.P for accounts receivable	0	0
Intercompany loan to affiliate	0	0
Other		0
Net cash used in investing activities	0	0
Cash flows from financing activities:
Distributions	0	0
Contributions from partners		0
Proceeds from increase in long-term debt	0	0
Payments on long-term debt	0	0
Net additions to (reductions in) short-term borrowings	0	0
Net additions to collateralized short-term borrowings	0	0
Net changes in advances with consolidated entities	5	5
Cash paid for financing costs	0	0
Net cash used in financing activities	5	5
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents - beginning of period	1	1
Cash and cash equivalents - end of period	1	1
Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	(35,000)	(27,000)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0	0
Capital expenditures	0	0
Proceeds from sale of assets	0	0
Cash collected for purchase of interest in accounts receivable	(985,084)	(803,109)
Cash remitted to Ferrellgas, L.P for accounts receivable	1,020,084	830,109
Intercompany loan to affiliate	(116,871)	35,232
Other		0
Net cash used in investing activities	(81,871)	62,232
Cash flows from financing activities:
Distributions	0	0
Contributions from partners		0
Proceeds from increase in long-term debt	0	0
Payments on long-term debt	0	0
Net additions to (reductions in) short-term borrowings	0	0
Net additions to collateralized short-term borrowings	0	0
Net changes in advances with consolidated entities	116,871	(35,232)
Cash paid for financing costs	0	0
Net cash used in financing activities	116,871	(35,232)
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents - beginning of period	0	0
Cash and cash equivalents - end of period	$ 0	$ 0