Guarantor financial information - Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 112,842	$ 15,075	$ 74,148
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(10,195)	(13,551)	(18,141)
Capital expenditures	(70,455)	(108,822)	(84,919)
Proceeds from sale of assets	4,472	5,699	152,587
Cash payments to construct assets in connection with future lease transactions	(37,042)	(9,934)	0
Cash receipts in connection with leased vehicles	41,924	862	0
Other	0	1,419	0
Net cash provided by (used in) investing activities	(71,296)	(124,327)	49,527
Cash flows from financing activities:
Distributions	0	(9,814)	(39,254)
Proceeds from issuance of long-term debt	703,750	0	323,680
Reductions on long-term debt	(285,857)	(2,428)	(212,920)
Net additions to (reductions in) short-term borrowings	(43,000)	10,200	(51,379)
Net additions to (reductions in) collateralized short-term borrowings	(62,000)	4,000	(11,000)
Cash paid for financing costs and other	(29,458)	(548)	(18,535)
Cash payments for principal portion of lease liability	(2,116)	0	0
Net cash provided by (used in) financing activities	281,161	995	(10,124)
Increase (decrease) in cash and cash equivalents	322,707	(108,257)	113,551
Cash and cash equivalents	333,761	11,054	119,311	$ 5,760
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(15,489)	(30,887)	(31,006)
Cash flows from investing activities:
Net cash provided by (used in) investing activities	15,496	40,706	70,246
Cash flows from financing activities:
Distributions		(9,814)	(39,254)
Cash paid for financing costs and other	(9)		(42)
Net cash provided by (used in) financing activities	(9)	(9,814)	(39,296)
Increase (decrease) in cash and cash equivalents	(2)	5	(56)
Cash and cash equivalents	6	8	3	59
Reportable Legal Entities [Member] | Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	75,882	25,796	139,294
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(10,195)	(13,551)	(18,141)
Capital expenditures	(70,455)	(108,822)	(81,114)
Proceeds from sale of assets	4,472	5,699	7,327
Cash payments to construct assets in connection with future lease transactions	(37,042)	(9,934)
Cash receipts in connection with leased vehicles	41,924	862
Cash collected from securitization of accounts receivable	0	0	0
Cash remitted for accounts receivable	0	0	0
Net changes in advances with consolidated entities		0	96,514
Intercompany loan to affiliate	(11,061)	24,328
Other		1,419
Net cash provided by (used in) investing activities	(82,357)	(99,999)	4,586
Cash flows from financing activities:
Distributions	(15,654)	(41,121)	(70,962)
Proceeds from issuance of long-term debt	703,750	(2,428)	323,680
Reductions on long-term debt	(285,857)		(212,920)
Net additions to (reductions in) short-term borrowings	(43,000)	10,200	(51,379)
Net additions to (reductions in) collateralized short-term borrowings	0	0	0
Net changes in advances with consolidated entities	0	0	0
Cash paid for financing costs and other	(29,449)	(536)	(18,493)
Cash payments for principal portion of lease liability	(2,116)
Net cash provided by (used in) financing activities	327,674	(33,885)	(30,074)
Increase (decrease) in cash and cash equivalents	321,199	(108,088)	113,806
Cash and cash equivalents	332,244	11,045	119,133	5,327
Reportable Legal Entities [Member] | Subsidiary Issuer [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(6)	(6)	(5)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0	0	0
Capital expenditures	0	0	0
Proceeds from sale of assets	0	0	0
Cash payments to construct assets in connection with future lease transactions	0	0
Cash receipts in connection with leased vehicles	0	0
Cash collected from securitization of accounts receivable	0	0	0
Cash remitted for accounts receivable	0	0	0
Net changes in advances with consolidated entities		0	0
Intercompany loan to affiliate	0	0
Other		0
Net cash provided by (used in) investing activities	0	0	0
Cash flows from financing activities:
Distributions	0	0	0
Proceeds from issuance of long-term debt	0		0
Reductions on long-term debt	0	0	0
Net additions to (reductions in) short-term borrowings	0	0	0
Net additions to (reductions in) collateralized short-term borrowings	0	0	0
Net changes in advances with consolidated entities	6	6	5
Cash paid for financing costs and other	0	0	0
Cash payments for principal portion of lease liability	0
Net cash provided by (used in) financing activities	6	6	5
Increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents	1	1	1	1
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	425	24,889	(48,708)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0	0	0
Capital expenditures	0	0	(3,805)
Proceeds from sale of assets	0	0	145,260
Cash payments to construct assets in connection with future lease transactions	0	0
Cash receipts in connection with leased vehicles	0	0
Cash collected from securitization of accounts receivable	0	0	0
Cash remitted for accounts receivable	0	0	0
Net changes in advances with consolidated entities		0	0
Intercompany loan to affiliate	0	0
Other		0
Net cash provided by (used in) investing activities	0	0	141,455
Cash flows from financing activities:
Distributions	0	0	0
Proceeds from issuance of long-term debt	0		0
Reductions on long-term debt	0	0	0
Net additions to (reductions in) short-term borrowings	0	0	0
Net additions to (reductions in) collateralized short-term borrowings	0	0	0
Net changes in advances with consolidated entities	(425)	(25,063)	(92,946)
Cash paid for financing costs and other	0	0	0
Cash payments for principal portion of lease liability	0
Net cash provided by (used in) financing activities	(425)	(25,063)	(92,946)
Increase (decrease) in cash and cash equivalents	0	(174)	(199)
Cash and cash equivalents	0	0	174	373
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(11,480)	(717)	3,573
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0	0	0
Capital expenditures	0	0	0
Proceeds from sale of assets	0	0	0
Cash payments to construct assets in connection with future lease transactions	0	0
Cash receipts in connection with leased vehicles	0	0
Cash collected from securitization of accounts receivable	841,142	1,258,050	1,226,211
Cash remitted for accounts receivable	(777,632)	(1,262,050)	(1,215,211)
Net changes in advances with consolidated entities		0	0
Intercompany loan to affiliate	0	0
Other		0
Net cash provided by (used in) investing activities	63,510	(4,000)	11,000
Cash flows from financing activities:
Distributions	0	0	0
Proceeds from issuance of long-term debt	0		0
Reductions on long-term debt	0	0	0
Net additions to (reductions in) short-term borrowings	0	0	0
Net additions to (reductions in) collateralized short-term borrowings	(62,000)	4,000	(11,000)
Net changes in advances with consolidated entities	11,480	729	(3,573)
Cash paid for financing costs and other	0	(12)	0
Cash payments for principal portion of lease liability	0
Net cash provided by (used in) financing activities	(50,520)	4,717	(14,573)
Increase (decrease) in cash and cash equivalents	1,510	0	0
Cash and cash equivalents	1,510	0	0	0
Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	63,510	(4,000)	11,000
Cash flows from investing activities:
Business acquisitions, net of cash acquired	0	0	0
Capital expenditures	0	0	0
Proceeds from sale of assets	0	0	0
Cash payments to construct assets in connection with future lease transactions	0	0
Cash receipts in connection with leased vehicles	0	0
Cash collected from securitization of accounts receivable	(841,142)	(1,258,050)	(1,226,211)
Cash remitted for accounts receivable	777,632	1,262,050	1,215,211
Net changes in advances with consolidated entities		0	(96,514)
Intercompany loan to affiliate	11,061	(24,328)
Other		0
Net cash provided by (used in) investing activities	(52,449)	(20,328)	(107,514)
Cash flows from financing activities:
Distributions	0	0	0
Proceeds from issuance of long-term debt	0		0
Reductions on long-term debt	0	0	0
Net additions to (reductions in) short-term borrowings	0	0	0
Net additions to (reductions in) collateralized short-term borrowings	0	0	0
Net changes in advances with consolidated entities	(11,061)	24,328	96,514
Cash paid for financing costs and other	0	0	0
Cash payments for principal portion of lease liability	0
Net cash provided by (used in) financing activities	(11,061)	24,328	96,514
Increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents	0	0	0	0
Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	128,331	45,962	105,154
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(10,195)	(13,551)	(18,141)
Capital expenditures	(70,455)	(108,822)	(84,919)
Proceeds from sale of assets	4,472	5,699	152,587
Cash payments to construct assets in connection with future lease transactions	(37,042)	(9,934)
Cash receipts in connection with leased vehicles	41,924	862
Cash collected from securitization of accounts receivable	0	0	0
Cash remitted for accounts receivable	0	0	0
Net changes in advances with consolidated entities		0	0
Intercompany loan to affiliate	0	0
Other		1,419
Net cash provided by (used in) investing activities	(71,296)	(124,327)	49,527
Cash flows from financing activities:
Distributions	(15,654)	(41,121)	(70,962)
Proceeds from issuance of long-term debt	703,750		323,680
Reductions on long-term debt	(285,857)	(2,428)	(212,920)
Net additions to (reductions in) short-term borrowings	(43,000)	10,200	(51,379)
Net additions to (reductions in) collateralized short-term borrowings	(62,000)	4,000	(11,000)
Net changes in advances with consolidated entities	0	0	0
Cash paid for financing costs and other	(29,449)	(548)	(18,493)
Cash payments for principal portion of lease liability	(2,116)
Net cash provided by (used in) financing activities	265,674	(29,897)	(41,074)
Increase (decrease) in cash and cash equivalents	322,709	(108,262)	113,607
Cash and cash equivalents	$ 333,755	$ 11,046	$ 119,308	$ 5,701