Guarantor financial information - Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2017	Oct. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 7,933	$ 54,550
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(13,867)	0
Capital expenditures	(20,154)	(10,005)
Proceeds from sale of assets	1,208	2,279
Net cash used in investing activities	(32,813)	(7,726)
Cash flows from financing activities:
Distributions	(9,813)	(50,294)
Proceeds from increase in long-term debt	23,580	25,626
Payments on long-term debt	(281)	(2,261)
Net additions to (reductions in) short-term borrowings	(5,879)	(4,467)
Net additions to collateralized short-term borrowings	19,000	10,000
Cash paid for financing costs	(287)	(1,390)
Net cash provided by (used in) financing activities	26,220	(39,150)
Increase (decrease) in cash and cash equivalents	1,340	7,674
Cash and cash equivalents - beginning of period	5,760	4,965
Cash and cash equivalents - end of period	7,100	12,639
Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	7,990	54,551
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(13,867)	0
Capital expenditures	(20,154)	(10,005)
Proceeds from sale of assets	1,208	2,279
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
Net cash used in investing activities	(32,813)	(7,726)
Cash flows from financing activities:
Distributions	(9,913)	(66,658)
Proceeds from increase in long-term debt	23,580	25,626
Payments on long-term debt	(281)	(2,261)
Net additions to (reductions in) short-term borrowings	(5,879)	(4,467)
Net additions to collateralized short-term borrowings	19,000	10,000
Net changes in advances with consolidated entities	0	0
Cash paid for financing costs	(287)	(1,390)
Net cash provided by (used in) financing activities	26,220	(39,150)
Increase (decrease) in cash and cash equivalents	1,397	7,675
Cash and cash equivalents - beginning of period	5,701	4,890
Cash and cash equivalents - end of period	7,098	12,565
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	23,305	79,220
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(13,867)
Capital expenditures	(19,429)	(10,000)
Proceeds from sale of assets	1,208	2,279
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	3,088	(14,453)
Net cash used in investing activities	(29,000)	(22,174)
Cash flows from financing activities:
Distributions	(9,913)	(66,658)
Proceeds from increase in long-term debt	23,580	25,626
Payments on long-term debt	(281)	(2,261)
Net additions to (reductions in) short-term borrowings	(5,879)	(4,467)
Net additions to collateralized short-term borrowings	0	0
Net changes in advances with consolidated entities	0	0
Cash paid for financing costs	(287)	(1,390)
Net cash provided by (used in) financing activities	7,220	(49,150)
Increase (decrease) in cash and cash equivalents	1,525	7,896
Cash and cash equivalents - beginning of period	5,327	4,472
Cash and cash equivalents - end of period	6,852	12,368
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(22,294)	(15,354)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0
Capital expenditures	(725)	(5)
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
Net cash used in investing activities	(725)	(5)
Cash flows from financing activities:
Distributions	0	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	22,891	15,138
Cash paid for financing costs	0	0
Net cash provided by (used in) financing activities	22,891	15,138
Increase (decrease) in cash and cash equivalents	(128)	(221)
Cash and cash equivalents - beginning of period	373	417
Cash and cash equivalents - end of period	245	196
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	25,981	687
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	203,291	183,939
Cash remitted to Ferrellgas, L.P for accounts receivable	(222,291)	(193,939)
Intercompany loan to affiliate	0	0
Net cash used in investing activities	(19,000)	(10,000)
Cash flows from financing activities:
Distributions	0	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	(19,000)	10,000
Net changes in advances with consolidated entities	(25,981)	(687)
Cash paid for financing costs	0	0
Net cash provided by (used in) financing activities	(6,981)	9,313
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	(2)	(2)
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
Net cash used in investing activities	0	0
Cash flows from financing activities:
Distributions	0	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	2	2
Cash paid for financing costs	0	0
Net cash provided by (used in) financing activities	2	2
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	(19,000)	(10,000)
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	(203,291)	(183,939)
Cash remitted to Ferrellgas, L.P for accounts receivable	222,291	193,939
Intercompany loan to affiliate	(3,088)	14,453
Net cash used in investing activities	15,912	24,453
Cash flows from financing activities:
Distributions	0	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	3,088	(14,453)
Cash paid for financing costs	0	0
Net cash provided by (used in) financing activities	3,088	(14,453)
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