Guarantor financial information - Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Jul. 31, 2018	Jul. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 70,777	$ 78,311
Cash flows from investing activities:
Payments to Acquire Businesses, Net of Cash Acquired	(11,351)	(14,862)
Payments to Acquire Productive Assets	(94,660)	(58,961)
Proceeds from sale of assets	2,416	57,802
Net cash used in investing activities	(103,595)	(16,021)
Cash flows from financing activities:
Distributions	(9,814)	(29,440)
Proceeds from increase in long-term debt	0	23,580
Reductions in Long-term Debt	(1,656)	(1,892)
Proceeds from (Repayments of) Short-term Debt	(32,800)	(84,179)
Net additions to collateralized short-term borrowings	4,000	35,000
Cash paid for financing costs	(531)	(1,161)
Net cash used in financing activities	(41,059)	(58,551)
Increase (decrease) in cash and cash equivalents	(73,877)	3,739
Cash and cash equivalents	45,434	9,499	$ 119,311	$ 5,760
Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	86,207	93,946
Cash flows from investing activities:
Payments to Acquire Businesses, Net of Cash Acquired	(11,351)	(14,862)
Payments to Acquire Productive Assets	(94,660)	(58,961)
Proceeds from sale of assets	2,416	57,802
Net cash used in investing activities	(103,595)	(16,021)
Cash flows from financing activities:
Distributions	(25,568)	(45,495)
Proceeds from increase in long-term debt		23,580
Reductions in Long-term Debt	(1,656)	(1,892)
Proceeds from (Repayments of) Short-term Debt	(32,800)	(84,179)
Net additions to collateralized short-term borrowings	4,000	35,000
Cash paid for financing costs	(531)	(1,149)
Net cash used in financing activities	(56,555)	(74,135)
Increase (decrease) in cash and cash equivalents	(73,943)	3,790
Cash and cash equivalents	45,365	9,491	119,308	5,701
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	111,008	65,604
Cash flows from investing activities:
Payments to Acquire Businesses, Net of Cash Acquired	(11,351)	(14,862)
Payments to Acquire Productive Assets	(94,660)	(57,158)
Proceeds from sale of assets	2,416	2,479
Net changes in advances with consolidated entities		116,871
Intercompany loan to affiliate	(20,638)
Net cash used in investing activities	(124,233)	47,330
Cash flows from financing activities:
Distributions	(25,568)	(45,495)
Proceeds from increase in long-term debt		23,580
Reductions in Long-term Debt	(1,656)	(1,892)
Proceeds from (Repayments of) Short-term Debt	(32,800)	(84,179)
Cash paid for financing costs	(520)	(1,149)
Net cash used in financing activities	(60,544)	(109,135)
Increase (decrease) in cash and cash equivalents	(73,769)	3,799
Cash and cash equivalents	45,364	9,126	119,133	5,327
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	(6)	(5)
Cash flows from financing activities:
Net changes in advances with consolidated entities	6	5
Net cash used in financing activities	6	5
Cash and cash equivalents	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	24,589	(3,531)
Cash flows from investing activities:
Payments to Acquire Productive Assets		(1,803)
Proceeds from sale of assets		55,323
Net cash used in investing activities		53,520
Cash flows from financing activities:
Net changes in advances with consolidated entities	(24,763)	(49,998)
Net cash used in financing activities	(24,763)	(49,998)
Increase (decrease) in cash and cash equivalents	(174)	(9)
Cash and cash equivalents		364	$ 174	$ 373
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	(45,384)	66,878
Cash flows from investing activities:
Cash collected for purchase of interest in accounts receivable	1,052,947	985,084
Cash remitted for accounts receivable	(1,056,947)	(1,020,084)
Net cash used in investing activities	(4,000)	(35,000)
Cash flows from financing activities:
Net additions to collateralized short-term borrowings	4,000	35,000
Net changes in advances with consolidated entities	45,395	(66,878)
Cash paid for financing costs	(11)
Net cash used in financing activities	49,384	(31,878)
Eliminations [Member] | Ferrellgas, L.P. [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(4,000)	(35,000)
Cash flows from investing activities:
Cash collected for purchase of interest in accounts receivable	(1,052,947)	(985,084)
Cash remitted for accounts receivable	1,056,947	1,020,084
Net changes in advances with consolidated entities		(116,871)
Intercompany loan to affiliate	20,638
Net cash used in investing activities	24,638	(81,871)
Cash flows from financing activities:
Net changes in advances with consolidated entities	(20,638)	116,871
Net cash used in financing activities	$ (20,638)	$ 116,871