BENEFIT PLANS: (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Interest cost on projected benefit obligation	$ 1,454	$ 1,681	$ 1,706
Expected return on assets	(1,596)	(1,675)	(1,565)
Plan expenses	226	220	227
Recognized net actuarial loss	1,802	1,145	1,155
Total cost recognized in pretax income	1,886	1,371	1,523
Cost recognized in pretax other comprehensive income	(1,185)	5,094	96
Net periodic pension cost	$ 701	$ 6,465	$ 1,619