Quarterly Results of Operations (Unaudited) (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
Quarterly Results of Operations (Unaudited)
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
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
Net (loss) income	8,057,000	11,216,000	1,655,000	(7,210,000)	(795,000)	3,869,000	8,738,000	(1,386,000)	13,718,000	10,426,000	30,451,000
Net (loss) income per share-basic (in dollars per share)	$ 0.36	$ 0.50	$ 0.07	$ (0.32)	$ (0.04)	$ 0.17	$ 0.40	$ (0.06)	$ 0.61	$ 0.47	$ 1.40
Net (loss) income per share-diluted (in dollars per share)	$ 0.35	$ 0.49	$ 0.07	$ (0.32)	$ (0.04)	$ 0.17	$ 0.39	$ (0.06)	$ 0.60	$ 0.47	$ 1.36
Quarterly Results of Operations
Reduction to income tax expense									(1,178,000)	(347,000)	(13,087,000)
R&D expense									25,515,000	37,214,000	30,977,000
Revision of annual incentive bonus accrual | Adjustment
Quarterly Results of Operations
Incentive bonus						4,300,000
Revision of estimate of annual effective income tax rate | Adjustment
Quarterly Results of Operations
Reduction to income tax expense						2,900,000
Tier II assets
Quarterly Results of Operations
Pre-tax impairment charges	3,300,000
UAS
Quarterly Results of Operations (Unaudited)
Revenue									208,810,000	194,276,000	273,728,000
Gross margin									80,818,000	79,082,000	116,065,000
Organizational realignment and workforce reduction, May 29, 2013
Quarterly Results of Operations
Severance costs				1,000,000
Organizational realignment and workforce reduction, September 26, 2013 | UAS
Quarterly Results of Operations
Severance costs			700,000
Global Observer Joint Capability Technology Demonstration contract
Quarterly Results of Operations
Revenue for the termination settlement of contract				2,300,000
Reimbursement of costs for contract						2,100,000
R&D expense						$ 2,100,000