Guarantor financial information - Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ (36,294)	$ 39,337
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(14,862)	0
Capital expenditures	(35,693)	(19,768)
Proceeds from sale of assets	4,207	4,591
Net cash used in investing activities	(46,348)	(15,214)
Cash flows from financing activities:
Distributions	(19,627)	(60,107)
Proceeds from increase in long-term debt	23,580	204,444
Payments on long-term debt	(1,267)	(172,790)
Net additions to (reductions in) short-term borrowings	(7,879)	(35,692)
Net additions to collateralized short-term borrowings	(97,000)	(69,000)
Cash paid for financing costs	(395)	(4,382)
Net cash provided by (used in) financing activities	91,055	(14,378)
Increase (decrease) in cash and cash equivalents	8,413	9,745
Cash and cash equivalents - beginning of period	5,760	4,965
Cash and cash equivalents - end of period	14,173	14,710
Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(20,841)	45,301
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(14,862)	0
Capital expenditures	(35,693)	(19,768)
Proceeds from sale of assets	4,207	4,591
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		(37)
Net cash used in investing activities	(46,348)	(15,214)
Cash flows from financing activities:
Distributions	(35,380)	(84,500)
Contributions from partners	0	167,640
Proceeds from increase in long-term debt	23,580	36,444
Payments on long-term debt	(1,267)	(172,790)
Net additions to (reductions in) short-term borrowings	(7,879)	(35,692)
Net additions to collateralized short-term borrowings	(97,000)	(69,000)
Net changes in advances with consolidated entities	0	0
Cash paid for financing costs	(395)	(1,422)
Net cash provided by (used in) financing activities	75,659	(21,320)
Increase (decrease) in cash and cash equivalents	8,470	8,767
Cash and cash equivalents - beginning of period	5,701	4,890
Cash and cash equivalents - end of period	14,171	13,657
Reportable Legal Entities [Member] | Ferrellgas, L.P. (Parent and Co-Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(57,734)	85,916
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(14,862)
Capital expenditures	(34,391)	(19,686)
Proceeds from sale of assets	4,207	4,591
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	132,748	28,408
Other		(37)
Net cash used in investing activities	87,702	13,276
Cash flows from financing activities:
Distributions	(35,380)	(84,500)
Contributions from partners		167,640
Proceeds from increase in long-term debt	23,580	36,444
Payments on long-term debt	(1,267)	(172,790)
Net additions to (reductions in) short-term borrowings	(7,879)	(35,692)
Net additions to collateralized short-term borrowings	0	0
Net changes in advances with consolidated entities	0	0
Cash paid for financing costs	(395)	(1,422)
Net cash provided by (used in) financing activities	(21,341)	(90,320)
Increase (decrease) in cash and cash equivalents	8,627	8,872
Cash and cash equivalents - beginning of period	5,327	4,472
Cash and cash equivalents - end of period	13,954	13,344
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	13,335	(47,221)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0
Capital expenditures	(1,302)	(82)
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	(1,302)	(82)
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	(12,190)	47,198
Cash paid for financing costs	0	0
Net cash provided by (used in) financing activities	(12,190)	47,198
Increase (decrease) in cash and cash equivalents	(157)	(105)
Cash and cash equivalents - beginning of period	373	417
Cash and cash equivalents - end of period	216	312
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	120,563	75,611
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0
Capital expenditures	0	0
Proceeds from sale of assets	0	0
Cash collected for purchase of interest in accounts receivable	574,783	469,600
Cash remitted to Ferrellgas, L.P for accounts receivable	(671,783)	(538,600)
Intercompany loan to affiliate	0	0
Other		0
Net cash used in investing activities	(97,000)	(69,000)
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	97,000	(69,000)
Net changes in advances with consolidated entities	(120,563)	(75,611)
Cash paid for financing costs	0	0
Net cash provided by (used in) financing activities	(23,563)	(6,611)
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 (used in) operating activities	(5)	(5)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	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 provided by (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 (used in) operating activities	(97,000)	(69,000)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0
Capital expenditures	0	0
Proceeds from sale of assets	0	0
Cash collected for purchase of interest in accounts receivable	(574,783)	(469,600)
Cash remitted to Ferrellgas, L.P for accounts receivable	671,783	538,600
Intercompany loan to affiliate	(132,748)	(28,408)
Other		0
Net cash used in investing activities	(35,748)	40,592
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	132,748	28,408
Cash paid for financing costs	0	0
Net cash provided by (used in) financing activities	132,748	28,408
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