Debt - Secured Credit Facilities (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jan. 31, 2019	Jul. 31, 2018
Debt Instrument [Line Items]
Short-term borrowings	$ 0	$ 32,800,000
Letters of credit outstanding	103,800,000	107,900,000
Term Loan Due 2023 May 4 [Member]
Debt Instrument [Line Items]
Aggregate principal amount	$ 275,000,000	$ 275,000,000
Term loan rate, as a percent	8.27%	7.86%
Revolving Facility Under Senior Secured Credit Facility Entered 2018 May [Member]
Debt Instrument [Line Items]
Available borrowing capacity	$ 196,200,000	$ 159,300,000
Short-term borrowings	0	$ 32,800,000
Credit facility interest rate		9.75%
Letter of Credit [Member]
Debt Instrument [Line Items]
Available borrowing capacity	21,200,000	$ 17,100,000
Ferrellgas, L.P. [Member]
Debt Instrument [Line Items]
Short-term borrowings	0	32,800,000
Letters of credit outstanding	103,800,000	107,900,000
Ferrellgas, L.P. [Member] | Term Loan Due 2023 May 4 [Member]
Debt Instrument [Line Items]
Aggregate principal amount	$ 275,000,000	$ 275,000,000
Term loan rate, as a percent	8.27%	7.86%
Ferrellgas, L.P. [Member] | Revolving Facility Under Senior Secured Credit Facility Entered 2018 May [Member]
Debt Instrument [Line Items]
Available borrowing capacity	$ 196,200,000	$ 159,300,000
Short-term borrowings	0	$ 32,800,000
Credit facility interest rate		9.75%
Ferrellgas, L.P. [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Available borrowing capacity	$ 21,200,000	$ 17,100,000