PROPERTY, PLANT AND EQUIPMENT: (Details) - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 34,345	$ 35,004
Less accumulated depreciation	(23,493)	(23,007)
Property, plant and equipment, net	10,852	11,997
Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	15,995	15,864
Furniture and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 18,350	$ 19,140