Income Taxes - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended	5 Months Ended	9 Months Ended	12 Months Ended
	Jan. 01, 2018	Apr. 30, 2018	Dec. 31, 2017	Apr. 30, 2018	Jul. 31, 2018	Jul. 31, 2017
Income Taxes [Line Items]
U.S. Federal statutory tax rate	21.00%	27.00%	35.00%
Discrete tax (benefit) provision		$ (1.4)		$ 5.5
Provisional estimate amount for one-time transition tax		1.3		5.8
Benefit for reversal of reserve expiration of the statute of limitations		0.6		0.6
Provisional amount of tax expense on remeasurement of deferred tax balance		0.2		$ 3.0
Provisional estimate amount for one-time transition tax, payment period				8 years
Unrecognized tax benefits, accrued interest and penalties		0.1		$ 0.1		$ 0.1
Unrecognized tax benefits, for uncertain tax positions		$ 4.0		$ 4.0
Scenario Forecast
Income Taxes [Line Items]
U.S. Federal statutory tax rate					27.00%