BENEFIT PLANS: (Details 6) - USD ($) $ in Thousands	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 23,708	$ 27,044	$ 29,120
Cash Equivalents [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,171	675
Equity Securities [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	15,878	18,634
Corporate Bonds And Debentures [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	6,663	7,735
Fair Value, Inputs, Level 1 [Member]
Changes in Fair Value of Plan Assets [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	17,049	19,309
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	1,171	675
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	15,878	18,634
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	6,663	7,735
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	6,663	7,735
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