Note N - Quarterly Results of Operations (Unaudited) (Details) - Quarterly Results of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Quarterly Results of Operations [Abstract]
Revenues	$ 137,611	$ 131,500	$ 133,834	$ 127,376	$ 122,624	$ 122,588	$ 121,431	$ 122,544	$ 530,321	$ 489,187
Gross profit	51,122	49,734	51,279	47,988	45,408	46,308	44,942	46,527	200,123	183,185
Net income	7,250	7,461	7,519	7,260	6,313	1,470	5,805	7,541	29,490	21,129
Net income attributable to common stockholders	$ 7,240	$ 7,451	$ 7,509	$ 7,250	$ 6,303	$ 1,460	$ 5,795	$ 7,531	$ 29,450	$ 21,089
Earnings per share:
Basic (in Dollars per share)	$ 0.85	$ 0.87	$ 0.87	$ 0.83	$ 0.72	$ 0.16	$ 0.64	$ 0.83	$ 3.42	$ 2.36	$ 3.53
Diluted (in Dollars per share)	$ 0.81	$ 0.82	$ 0.83	$ 0.79	$ 0.68	$ 0.16	$ 0.61	$ 0.79	$ 3.25	$ 2.25	$ 3.36