BENEFIT PLANS: (Details 7) - USD ($) $ in Thousands	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 27,044	$ 29,120	$ 24,777
Cash Equivalents [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	675	2,466
Equity Securities [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	18,634	18,844
Corporate Bonds And Debentures [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	7,735	7,810
Fair Value, Inputs, Level 1 [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	19,309	21,310
Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	675	2,466
Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	18,634	18,844
Fair Value, Inputs, Level 1 [Member] | Corporate Bonds And Debentures [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Fair Value, Inputs, Level 2 [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	7,735	7,810
Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Fair Value, Inputs, Level 2 [Member] | Corporate Bonds And Debentures [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	7,735	7,810
Fair Value, Inputs, Level 3 [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Fair Value, Inputs, Level 3 [Member] | Corporate Bonds And Debentures [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 0	$ 0