BENEFIT PLANS: (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Change in benefit obligation:
Benefit obligation at beginning of year	$ 37,899	$ 34,550	$ 32,568
Interest cost	1,454	1,681	1,706
Actuarial (gain) loss	1,802	1,145	1,155
Benefits paid	(2,307)	(2,324)	(2,585)
Benefit obligation at end of year	38,582	37,899	34,550
Change in plan assets:
Fair value of plan assets at beginning of year	20,222	21,931	20,493
Company contributions	4,572	1,407	1,075
Actual return on plan assets	2,523	(568)	3,168
Benefits paid	(2,307)	(2,324)	(2,585)
Plan expenses	(233)	(224)	(220)
Fair value of plan assets at end of year	24,777	20,222	21,931
Funded (underfunded) status:	(13,805)	(17,677)	(12,619)
Recognition of underfunded status:
Accrued pension cost	$ (4,572)	$ (1,407)	$ (1,075)