CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Revenue:
Product sales	$ 194,996	$ 139,813	$ 179,537
Contract services	56,707	100,339	145,471
Total revenue	251,703	240,152	325,008
Cost of sales:
Product sales	119,137	85,643	104,347
Contract services	38,953	61,973	91,328
Total cost of sales	158,090	147,616	195,675
Gross margin	93,613	92,536	129,333
Selling, general and administrative	55,679	51,520	55,280
Research and development	25,515	37,214	30,977
Income from operations	12,419	3,802	43,076
Other income:
Interest income	855	726	462
Other income	1,622	6,245
Income before income taxes	14,896	10,773	43,538
Provision for income taxes	1,178	347	13,087
Net income	$ 13,718	$ 10,426	$ 30,451
Earnings per share data:
Basic (in dollars per share)	$ 0.61	$ 0.47	$ 1.40
Diluted (in dollars per share)	$ 0.60	$ 0.47	$ 1.36
Weighted average shares outstanding:
Basic (in shares)	22,354,444	22,069,842	21,783,496
Diluted (in shares)	22,719,218	22,390,420	22,315,474