CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Revenue:
Product sales	$ 179,537	$ 137,724	$ 103,268
Contract services	145,471	154,779	146,250
Total revenue	325,008	292,503	249,518
Cost of sales:
Product sales	104,347	74,843	59,266
Contract services	91,328	100,509	93,426
Total cost of sales	195,675	175,352	152,692
Gross margin	129,333	117,151	96,826
Selling, general and administrative	55,280	47,431	42,429
Research and development	30,977	35,769	24,510
Income from operations	43,076	33,951	29,887
Other income:
Interest income	462	277	195
Income before income taxes	43,538	34,228	30,082
Provision for income taxes	13,087	8,319	9,366
Net income	$ 30,451	$ 25,909	$ 20,716
Earnings per share data:
Basic (in dollars per share)	$ 1.40	$ 1.20	$ 0.97
Diluted (in dollars per share)	$ 1.36	$ 1.17	$ 0.94
Weighted average shares outstanding:
Basic (in shares)	21,783,496	21,591,333	21,391,795
Diluted (in shares)	22,315,474	22,081,266	21,977,364