Guarantor financial information - Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jan. 31, 2020	Jan. 31, 2020	Jan. 31, 2019	Jul. 31, 2019	Jul. 31, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		$ 568	$ (55,118)
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(6,400)	(5,069)
Capital expenditures		(33,422)	(58,330)
Proceeds from sale of assets		1,659	1,960
Cash payments to construct assets in connection with future lease transactions		(30,307)
Cash receipts in connection with leased vehicles		19,929
Net cash used in investing activities		(48,541)	(61,439)
Cash flows from financing activities:
Distributions			(9,814)
Payments on long-term debt		(972)	(1,014)
Net reductions in short-term borrowings		(3,000)	(32,800)
Net additions to collateralized short-term borrowings		59,000	82,000
Cash payments for principal portion of lease liability	$ (266)	(294)
Cash paid for financing costs and other		(4,245)	(221)
Net cash provided by financing activities		50,625	37,893
Increase (decrease) in cash and cash equivalents		2,652	(78,664)
Cash and cash equivalents	13,706	13,706	40,647	$ 11,054	$ 119,311
Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		16,000	(39,714)
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(6,400)	(5,069)
Capital expenditures		(33,422)	(58,330)
Proceeds from sale of assets		1,659	1,960
Cash payments to construct assets in connection with future lease transactions		(30,307)
Cash receipts in connection with leased vehicles		19,929
Net cash used in investing activities		(48,541)	(61,439)
Cash flows from financing activities:
Distributions		(15,654)	(25,568)
Payments on long-term debt		(972)	(1,014)
Net reductions in short-term borrowings		(3,000)	(32,800)
Net additions to collateralized short-term borrowings		59,000	82,000
Cash payments for principal portion of lease liability	(266)	(294)
Cash paid for financing costs and other		(4,236)	(221)
Net cash provided by financing activities		35,138	22,397
Increase (decrease) in cash and cash equivalents		2,597	(78,756)
Cash and cash equivalents	13,643	13,643	40,552	11,046	119,308
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		80,433	98,494
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(6,400)	(5,069)
Capital expenditures		(33,422)	(58,330)
Proceeds from sale of assets		1,659	1,960
Cash payments to construct assets in connection with future lease transactions		(30,307)
Cash receipts in connection with leased vehicles		19,929
Net changes in advances with consolidated entities			(56,291)
Intercompany loan to affiliate		(5,433)
Net cash used in investing activities		(53,974)	(117,730)
Cash flows from financing activities:
Distributions		(15,654)	(25,568)
Payments on long-term debt		(972)	(1,014)
Net reductions in short-term borrowings		(3,000)	(32,800)
Cash paid for financing costs and other		(4,236)	(210)
Net cash provided by financing activities		(23,862)	(59,592)
Increase (decrease) in cash and cash equivalents		2,597	(78,828)
Cash and cash equivalents	13,642	13,642	40,305	11,045	119,133
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Subsidiary Issuer [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		(4)	(5)
Cash flows from financing activities:
Net changes in advances with consolidated entities		4	5
Net cash provided by financing activities		4	5
Cash and cash equivalents	$ 1	1	1	$ 1	1
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		512	24,696
Cash flows from financing activities:
Net changes in advances with consolidated entities		(512)	(24,624)
Net cash provided by financing activities		(512)	(24,624)
Increase (decrease) in cash and cash equivalents			72
Cash and cash equivalents			246		$ 174
Reportable Legal Entities [Member] | Ferrellgas, L.P. [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		(5,941)	(80,899)
Cash flows from investing activities:
Cash collected from securitization of accounts receivable		416,325	710,497
Cash remitted for accounts receivable		(475,325)	(792,497)
Net cash used in investing activities		(59,000)	(82,000)
Cash flows from financing activities:
Net additions to collateralized short-term borrowings		59,000	82,000
Net changes in advances with consolidated entities		5,941	80,910
Cash paid for financing costs and other			(11)
Net cash provided by financing activities		64,941	162,899
Eliminations [Member] | Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		(59,000)	(82,000)
Cash flows from investing activities:
Cash collected from securitization of accounts receivable		(416,325)	(710,497)
Cash remitted for accounts receivable		475,325	792,497
Net changes in advances with consolidated entities			56,291
Intercompany loan to affiliate		5,433
Net cash used in investing activities		64,433	138,291
Cash flows from financing activities:
Net changes in advances with consolidated entities		(5,433)	(56,291)
Net cash provided by financing activities		$ (5,433)	$ (56,291)