Income Taxes (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Jan. 31, 2018	Apr. 30, 2018	Apr. 30, 2018	Apr. 30, 2017
Tax Credit Carryforward [Line Items]
Provisional expense	$ 1.6	$ 1.0
State [Member]
Tax Credit Carryforward [Line Items]
Gross amount of state tax credit carryforwards		5.2	$ 5.2	$ 6.1
Net deferred tax assets related to tax credit carryforwards		1.5	1.5	1.6
State [Member] | Other Liabilities [Member]
Tax Credit Carryforward [Line Items]
Net deferred tax assets related to tax credit carryforwards		$ 1.3	1.3	$ 1.5
Investment Tax Credit Carryforward [Member] | State [Member]
Tax Credit Carryforward [Line Items]
Decrease in valuation allowance			$ 0.0