Note 5 - Net Income Per Common Share (Details) - Earnings Per Share, Basic and Diluted (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Basic
Net income (in Dollars)	$ 22,816	$ 14,669	$ 41,319	$ 55,710	$ 23,272	$ 15,463	$ 32,859	$ 39,031	$ 134,514	$ 110,625	$ 116,791
Weighted average shares outstanding-basic									38,457,680	38,297,083	38,068,001
Plus effect of stock options and restricted stock units									410,726	322,993	323,703
Weighted-average shares outstanding-diluted									38,868,406	38,620,076	38,391,704
Diluted earnings per common share (in Dollars per share)	$ 0.59	$ 0.38	$ 1.06	$ 1.43	$ 0.60	$ 0.40	$ 0.85	$ 1.01	$ 3.46	$ 2.86	$ 3.04
Basic earnings per common share (in Dollars per share)	$ 0.59	$ 0.38	$ 1.07	$ 1.45	$ 0.61	$ 0.40	$ 0.86	$ 1.02	$ 3.50	$ 2.89	$ 3.07