Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Tax Credit Carryforward [Line Items]
Effective income tax rate	33.20%	35.70%	34.50%	36.10%
Excess tax benefit related to stock-based compensation			$ 1.3
Investment Tax Credit Carryforward | State
Tax Credit Carryforward [Line Items]
Valuation allowance		$ 0.4		$ 0.4