Guarantor financial information - Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Apr. 30, 2020	Apr. 30, 2020	Apr. 30, 2019	Jul. 31, 2019	Jul. 31, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		$ 98,294	$ 70,777
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(6,400)	(11,351)
Capital expenditures		(57,251)	(94,660)
Proceeds from sale of assets		2,510	2,416
Cash payments to construct assets in connection with future lease transactions		(37,042)
Cash receipts in connection with leased vehicles		21,995
Net cash used in investing activities		(76,188)	(103,595)
Cash flows from financing activities:
Distributions			(9,814)
Proceeds from issuance of long-term debt		703,750
Reductions on long-term debt		(285,285)	(1,656)
Net reductions in short-term borrowings		(43,000)	(32,800)
Net additions to (reductions on) collateralized short-term borrowings		(62,000)	4,000
Cash payments for principal portion of lease liability	$ (650)	(944)
Cash paid for financing costs and other		(27,620)	(531)
Net cash provided by (used in) financing activities		285,687	(41,059)
Increase (decrease) in cash and cash equivalents		307,793	(73,877)
Cash and cash equivalents	318,847	318,847	45,434	$ 11,054	$ 119,311
Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		113,779	86,207
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(6,400)	(11,351)
Capital expenditures		(57,251)	(94,660)
Proceeds from sale of assets		2,510	2,416
Cash payments to construct assets in connection with future lease transactions		(37,042)
Cash receipts in connection with leased vehicles		21,995
Net cash used in investing activities		(76,188)	(103,595)
Cash flows from financing activities:
Distributions		(15,654)	(25,568)
Proceeds from issuance of long-term debt		703,750
Reductions on long-term debt		(285,285)	(1,656)
Net reductions in short-term borrowings		(43,000)	(32,800)
Net additions to (reductions on) collateralized short-term borrowings		(62,000)	4,000
Cash payments for principal portion of lease liability	(650)	(944)
Cash paid for financing costs and other		(27,611)	(531)
Net cash provided by (used in) financing activities		270,200	(56,555)
Increase (decrease) in cash and cash equivalents		307,791	(73,943)
Cash and cash equivalents	318,837	318,837	45,365	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		60,132	111,008
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(6,400)	(11,351)
Capital expenditures		(57,251)	(94,660)
Proceeds from sale of assets		2,510	2,416
Cash payments to construct assets in connection with future lease transactions		(37,042)
Cash receipts in connection with leased vehicles		21,995
Intercompany loan to affiliate		(8,353)	(20,638)
Net cash used in investing activities		(84,541)	(124,233)
Cash flows from financing activities:
Distributions		(15,654)	(25,568)
Proceeds from issuance of long-term debt		703,750
Reductions on long-term debt		(285,285)	(1,656)
Net reductions in short-term borrowings		(43,000)	(32,800)
Cash paid for financing costs and other		(27,611)	(520)
Net cash provided by (used in) financing activities		332,200	(60,544)
Increase (decrease) in cash and cash equivalents		307,791	(73,769)
Cash and cash equivalents	318,836	318,836	45,364	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)	(6)
Cash flows from financing activities:
Net changes in advances with consolidated entities		4	6
Net cash provided by (used in) financing activities		4	6
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		513	24,589
Cash flows from financing activities:
Net changes in advances with consolidated entities		(513)	(24,763)
Net cash provided by (used in) financing activities		(513)	(24,763)
Increase (decrease) in cash and cash equivalents			(174)
Cash and cash equivalents					$ 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		(8,862)	(45,384)
Cash flows from investing activities:
Cash collected from securitization of accounts receivable		685,640	1,052,947
Cash remitted for accounts receivable		(623,640)	(1,056,947)
Net cash used in investing activities		62,000	(4,000)
Cash flows from financing activities:
Net additions to (reductions on) collateralized short-term borrowings		(62,000)	4,000
Net changes in advances with consolidated entities		8,862	45,395
Cash paid for financing costs and other			(11)
Net cash provided by (used in) financing activities		(53,138)	49,384
Eliminations [Member] | Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		62,000	(4,000)
Cash flows from investing activities:
Cash collected from securitization of accounts receivable		(685,640)	(1,052,947)
Cash remitted for accounts receivable		623,640	1,056,947
Intercompany loan to affiliate		8,353	20,638
Net cash used in investing activities		(53,647)	24,638
Cash flows from financing activities:
Net changes in advances with consolidated entities		(8,353)	(20,638)
Net cash provided by (used in) financing activities		$ (8,353)	$ (20,638)