INTANGIBLE AND OTHER ASSETS: (Details) - USD ($) $ in Thousands	Apr. 30, 2015	Apr. 30, 2014
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Cost	$ 21,197	$ 21,997
Finite-Lived Intangible Assets, Accumulated Amortization	10,757	9,354
Customer Contracts and Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Cost	16,986	16,986
Finite-Lived Intangible Assets, Accumulated Amortization	10,757	9,342
Prepaid Expenses [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Cost	2,520	3,019
Finite-Lived Intangible Assets, Accumulated Amortization	0	0
Deferred Order Entry Costs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Cost	961	1,168
Finite-Lived Intangible Assets, Accumulated Amortization	0	0
Other [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Cost	730	824
Finite-Lived Intangible Assets, Accumulated Amortization	$ 0	$ 12