Debt Debt (Consolidated Interest Coverage Ratio) (Details)	3 Months Ended	12 Months Ended
	Jan. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Apr. 30, 2018
Debt Instrument, Covenant Description	24.9
current consolidated interest coverage ratio	214.00%
Debt Instrument, Covenant Compliance	193.2	67.5
Maximum [Member]
required consolidated interest coverage ratio	175.00%		250.00%	175.00%
Ferrellgas, L.P. [Member]
Debt Instrument, Covenant Description	24.9
current consolidated interest coverage ratio	214.00%
Debt Instrument, Covenant Compliance	193.2	67.5
Ferrellgas, L.P. [Member] | Maximum [Member]
required consolidated interest coverage ratio	175.00%		250.00%	175.00%
Interest Coverage Covenant [Member]
Debt Instrument, Covenant Description	44.3
Debt Instrument, Covenant Compliance	25.3
Interest Coverage Covenant [Member] | Ferrellgas, L.P. [Member]
Debt Instrument, Covenant Description	44.3
Debt Instrument, Covenant Compliance	25.3