BENEFIT PLANS: (Details 6) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Fair value of plan assets at beginning of year	$ 24,777	$ 20,222	$ 21,931	$ 20,493
Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets at beginning of year	18,560	17,780
Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets at beginning of year	6,217	2,442
Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets at beginning of year	0	0
Cash Equivalents [Member]
Fair value of plan assets at beginning of year	1,251	780
Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets at beginning of year	1,251	780
Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets at beginning of year	0	0
Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets at beginning of year	0	0
Equity Securities [Member]
Fair value of plan assets at beginning of year	16,669	15,376
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets at beginning of year	16,669	15,376
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets at beginning of year	0	0
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets at beginning of year	0	0
Corporate Bonds and Debentures [Member]
Fair value of plan assets at beginning of year	6,215	1,773
Corporate Bonds and Debentures [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets at beginning of year	0	0
Corporate Bonds and Debentures [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets at beginning of year	6,215	1,773
Corporate Bonds and Debentures [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets at beginning of year	0	0
US Treasury Securities [Member]
Fair value of plan assets at beginning of year	642	2,293
US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets at beginning of year	640	1,624
US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets at beginning of year	2	669
US Treasury Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets at beginning of year	$ 0	$ 0