Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	4 Months Ended	8 Months Ended	9 Months Ended		12 Months Ended
	Jan. 31, 2018	Apr. 30, 2018	Dec. 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Apr. 30, 2018	Apr. 30, 2017
U.S. corporate income tax rate (as a percent)			35.00%
Provisional income tax benefit	$ 7.8			$ 7.8
Effective income tax rate (as a percent)				22.70%	26.10%
Decrease in deferred tax liabilities and tax expense					$ 7.0
Valuation allowance	$ 0.3			$ 0.3			$ 0.3
Forecast
U.S. corporate income tax rate (as a percent)		21.00%				30.40%