CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Revenue:
Product sales	$ 139,813	$ 179,537	$ 137,724
Contract services	100,339	145,471	154,779
Total revenue	240,152	325,008	292,503
Cost of sales:
Product sales	85,643	104,347	74,843
Contract services	61,973	91,328	100,509
Total cost of sales	147,616	195,675	175,352
Gross margin	92,536	129,333	117,151
Selling, general and administrative	51,520	55,280	47,431
Research and development	37,214	30,977	35,769
Income from operations	3,802	43,076	33,951
Other income:
Interest income	726	462	277
Other income	6,245
Income before income taxes	10,773	43,538	34,228
Provision for income taxes	347	13,087	8,319
Net income	$ 10,426	$ 30,451	$ 25,909
Earnings per share data:
Basic (in dollars per share)	$ 0.47	$ 1.40	$ 1.20
Diluted (in dollars per share)	$ 0.47	$ 1.36	$ 1.17
Weighted average shares outstanding:
Basic (in shares)	22,069,842	21,783,496	21,591,333
Diluted (in shares)	22,390,420	22,315,474	22,081,266