Guarantor financial information - Statements of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jul. 31, 2020	Jul. 31, 2019
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 44,451	$ 568
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(6,400)
Capital expenditures	(35,333)	(33,422)
Proceeds from sale of assets	3,144	1,659
Cash payments to construct assets in connection with future lease transactions		(30,307)
Cash receipts in connection with leased vehicles		19,929
Net cash provided by (used in) investing activities	(32,189)	(48,541)
Cash flows from financing activities:
Cash paid for financing costs	(14,960)	(3,925)
Payments on long-term debt	(1,120)	(972)
Net additions to (reductions in) short-term borrowings		(3,000)
Net additions to (reductions in) collateralized short-term borrowings		59,000
Cash payments for principal portion of lease liability	(3,460)	(320)
Cash paid for financing costs	(14,960)	(3,925)
Net cash provided by (used in) financing activities	(19,540)	50,625
Increase (decrease) in cash and cash equivalents	(7,278)	2,652
Cash and cash equivalents	326,483	13,706	$ 333,761	$ 11,054
Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	44,451	16,000
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(6,400)
Capital expenditures	(35,333)	(33,422)
Proceeds from sale of assets	3,144	1,659
Cash payments to construct assets in connection with future lease transactions		(30,307)
Cash receipts in connection with leased vehicles		19,929
Loan to Ferrellgas Partners, L.P.	(19,900)
Net cash provided by (used in) investing activities	(52,089)	(48,541)
Cash flows from financing activities:
Distributions		(15,654)
Cash paid for financing costs	(14,960)	(3,916)
Payments on long-term debt	(1,120)	(972)
Net additions to (reductions in) short-term borrowings		(3,000)
Net additions to (reductions in) collateralized short-term borrowings		59,000
Cash payments for principal portion of lease liability	(3,460)	(320)
Cash paid for financing costs	(14,960)	(3,916)
Cash paid for financing costs and other		(4,236)
Net cash provided by (used in) financing activities	(19,540)	35,138
Increase (decrease) in cash and cash equivalents	(27,178)	2,597
Cash and cash equivalents	306,577	13,643	333,755	11,046
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	44,691	80,433
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(6,400)
Capital expenditures	(35,333)	(33,422)
Proceeds from sale of assets	3,144	1,659
Cash payments to construct assets in connection with future lease transactions		(30,307)
Cash receipts in connection with leased vehicles		19,929
Intercompany loan to affiliate	(4,870)
Loan to Ferrellgas Partners, L.P.	(19,900)	(5,433)
Net cash provided by (used in) investing activities	(56,959)	(53,974)
Cash flows from financing activities:
Distributions		(15,654)
Cash paid for financing costs	(14,960)
Payments on long-term debt	(1,120)	(972)
Net additions to (reductions in) short-term borrowings		(3,000)
Cash payments for principal portion of lease liability	(3,460)
Cash paid for financing costs	(14,960)
Cash paid for financing costs and other		(4,236)
Net cash provided by (used in) financing activities	(19,540)	(23,862)
Increase (decrease) in cash and cash equivalents	(31,808)	2,597
Cash and cash equivalents	300,436	13,642	332,244	11,045
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Subsidiary Issuer [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(6)	(4)
Cash flows from financing activities:
Net changes in advances with consolidated entities	6	4
Net cash provided by (used in) financing activities	6	4
Cash and cash equivalents	1	1	1	$ 1
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(9)	512
Cash flows from financing activities:
Net changes in advances with consolidated entities	9	(512)
Net cash provided by (used in) financing activities	9	(512)
Ferrellgas, L.P. [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(4,856)	(5,941)
Cash flows from investing activities:
Cash collected from securitization of accounts receivable	422,498	416,325
Cash remitted for accounts receivable	(417,867)	(475,325)
Net cash provided by (used in) investing activities	4,631	(59,000)
Cash flows from financing activities:
Net additions to (reductions in) collateralized short-term borrowings		59,000
Net changes in advances with consolidated entities	4,855	5,941
Net cash provided by (used in) financing activities	4,855	64,941
Increase (decrease) in cash and cash equivalents	4,630
Cash and cash equivalents	6,140		$ 1,510
Ferrellgas, L.P. [Member] | Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	4,631	(59,000)
Cash flows from investing activities:
Cash collected from securitization of accounts receivable	(422,498)	(416,325)
Cash remitted for accounts receivable	417,867	475,325
Intercompany loan to affiliate	4,870
Loan to Ferrellgas Partners, L.P.		5,433
Net cash provided by (used in) investing activities	239	64,433
Cash flows from financing activities:
Net changes in advances with consolidated entities	(4,870)	(5,433)
Net cash provided by (used in) financing activities	$ (4,870)	$ (5,433)