Benefit Plans (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Benefit Plans [Line Items]
401(k) expense	$ 3,681	$ 3,049	$ 2,964
Common stock held for future issuance	1,520,985
Executive officers participants in SERP	2
Annual retirement benefit maximum percentage of base compensation for executives until death	50.00%
Deferred compensation accrued	6,611	6,574
Defined benefit plan discount rate	4.60%	5.50%
Expected retirement benefit expense for the next five years	625
Executive Officers [Member]
Benefit Plans [Line Items]
Retirement benefit expense	$ 662	$ 0	$ 0