Stock-Based Compensation (Stock-Based Compensation Expense Allocated) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 897	$ 827	$ 2,506	$ 2,477
Cost of Sales and Distribution [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	256	160	777	468
Selling and Marketing Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	183	253	385	755
General and Administrative Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 458	$ 414	$ 1,344	$ 1,254