Preferred And Common Stock (Stock Option Activity) (Details) (USD $)	1 Months Ended	12 Months Ended
	Jun. 30, 2011	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Preferred And Common Stock [Line Items]
Number of Shares, Exercised		(159,600)	(184,441)	(83,450)
Weighted Average Exercise Price, Outstanding		23.38	22.78	20.45
Weighted Average Exercise Price, Granted		44.39	0.00	25.27
Weighted Average Exercise Price, Exercised		20.36	20.24	14.85
Weighted Average Exercise Price, Forfeited		36.19	0.00	24.41
Weighted Average Exercise Price, Outstanding at January 31, 2012		32.59	23.38	22.78
Restricted Stock Units (RSUs) [Member]
Preferred And Common Stock [Line Items]
Number of Shares, Outstanding		28,000
Number of Shares, Granted	15,000	38,198	28,000
Number of Shares, Exercised
Number of Shares, Forfeited
Number of Shares, Outstanding		66,198	28,000
Stock Options [Member]
Preferred And Common Stock [Line Items]
Number of Shares, Outstanding		775,109	959,550	678,000
Number of Shares, Granted		441,000		377,000
Number of Shares, Exercised		(159,600)	(184,441)	(83,450)
Number of Shares, Forfeited		(3,000)		(12,000)
Number of Shares, Outstanding		1,053,509	775,109	959,550