Segment Data (Details) (USD $)	3 Months Ended								12 Months Ended
	Apr. 30, 2014	Jan. 25, 2014	Oct. 26, 2013	Jul. 27, 2013	Apr. 30, 2013	Jan. 26, 2013	Oct. 27, 2012	Jul. 28, 2012	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Segment Data
Revenue	$ 73,498,000	$ 69,221,000	$ 64,867,000	$ 44,117,000	$ 54,110,000	$ 47,087,000	$ 80,278,000	$ 58,677,000	$ 251,703,000	$ 240,152,000	$ 325,008,000
Cost of sales									158,090,000	147,616,000	195,675,000
Gross margin	30,138,000	27,052,000	23,878,000	12,545,000	17,722,000	19,673,000	35,636,000	19,505,000	93,613,000	92,536,000	129,333,000
Selling, general and administrative									55,679,000	51,520,000	55,280,000
Research and development									25,515,000	37,214,000	30,977,000
Income from operations									12,419,000	3,802,000	43,076,000
Interest income									855,000	726,000	462,000
Other income									1,622,000	6,245,000
Income before income taxes									14,896,000	10,773,000	43,538,000
Inter-segment and corporate elimination
Segment Data
Revenue									0	0	0
UAS
Segment Data
Revenue									208,810,000	194,276,000	273,728,000
Cost of sales									127,992,000	115,194,000	157,663,000
Gross margin									80,818,000	79,082,000	116,065,000
EES
Segment Data
Revenue									42,893,000	45,876,000	51,280,000
Cost of sales									30,098,000	32,422,000	38,012,000
Gross margin									$ 12,795,000	$ 13,454,000	$ 13,268,000