Organization and Significant Accounting Policies Other (Details)	3 Months Ended								12 Months Ended
	Apr. 30, 2016 USD ($)	Jan. 30, 2016 USD ($)	Oct. 31, 2015 USD ($)	Aug. 01, 2015 USD ($)	Apr. 30, 2015 USD ($)	Jan. 31, 2015 USD ($)	Nov. 01, 2014 USD ($)	Aug. 02, 2014 USD ($)	Apr. 30, 2016 USD ($) item shares	Apr. 30, 2015 USD ($) shares	Apr. 30, 2014 USD ($) shares
Self-Insurance Liability
Estimated self-insurance liability of employee medical claim	$ 1,176,000				$ 1,293,000				$ 1,176,000	$ 1,293,000
Revenue Recognition
Number of key factors that impact reliability of management's estimates for revenue recognition | item									2
Maximum term of contract, considered as a factor in management estimates									6 months
Research and Development
Revenue from customer-funded R&D									$ 53,546,000	36,998,000	$ 28,393,000
Cost of sales									34,786,000	24,776,000	18,644,000
Deferred Rent Credit, Noncurrent	1,714,000				1,381,000				1,714,000	1,381,000
Advertising Costs
Advertising expenses									486,000	416,000	225,000
Numerator for basic earnings per share:
Net income	$ 5,364,000	$ 6,164,000	$ 4,419,000	$ (6,981,000)	$ 7,080,000	$ 2,325,000	$ (2,901,000)	$ (3,609,000)	$ 8,966,000	$ 2,895,000	$ 13,718,000
Denominator for basic earnings (loss) per share:
Weighted average common shares outstanding, excluding unvested restricted stock (in shares) | shares									22,936,413	22,868,733	22,354,444
Dilutive effect of employee stock options and unvested restricted stock (in shares) | shares									217,080	277,264	364,774
Denominator for diluted earnings (loss) per share (in shares) | shares									23,153,493	23,145,997	22,719,218
Number of shares reserved for issuance that are anti-dilutive | shares									22,000	43,000	51,000