Segment Data (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Apr. 30, 2013	Jan. 26, 2013	Oct. 27, 2012	Jul. 28, 2012	Apr. 30, 2012	Jan. 28, 2012	Oct. 29, 2011	Jul. 30, 2011	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Segment Data
Intersegment sales									$ 0
Revenue:
Total revenue	54,110	47,087	80,278	58,677	110,675	71,964	80,372	61,997	240,152	325,008	292,503
Cost of sales:
Total cost of sales									147,616	195,675	175,352
Gross margin:
Gross margin	17,722	19,673	35,636	19,505	49,555	27,433	30,630	21,715	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
Interest income									726	462	277
Other income									6,245
Income before income taxes									10,773	43,538	34,228
Geographic Information
Sales to non-U.S. customers as percentage of revenue									15.00%	5.00%	7.00%
UAS
Revenue:
Total revenue									194,276	273,728	249,769
Cost of sales:
Total cost of sales									115,194	157,663	150,256
Gross margin:
Gross margin									79,082	116,065	99,513
EES
Revenue:
Total revenue									45,876	51,280	42,734
Cost of sales:
Total cost of sales									32,422	38,012	25,096
Gross margin:
Gross margin									13,454	13,268	17,638
Unallocated to segment
Gross margin:
Selling, general and administrative									51,520	55,280	47,431
Research and development									37,214	30,977	35,769
Interest income									726	462	277
Other income									$ 6,245