1. Summary of Accounting Policies (Details) - USD ($)	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	May 01, 2018
1. Summary of Accounting Policies (Details) [Line Items]
Contract with Customer, Liability, Revenue Recognized	$ 45,300,000
Revenues	49,509,000	$ 39,407,000
Operating Lease, Right-of-Use Asset	13,200,000
Operating Lease, Liability	$ 13,400,000
Certification Marks [Member]
1. Summary of Accounting Policies (Details) [Line Items]
Finite-Lived Intangible Asset, Useful Life	3 years
Building [Member]
1. Summary of Accounting Policies (Details) [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Minimum [Member] | Other Depreciable Assets [Member]
1. Summary of Accounting Policies (Details) [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Maximum [Member] | Other Depreciable Assets [Member]
1. Summary of Accounting Policies (Details) [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Accounting Standards Update 2014-09 [Member]
1. Summary of Accounting Policies (Details) [Line Items]
Revenues	$ 2,662,000
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets			$ 484,000
Liabilities, Total [Member] | Accounting Standards Update 2014-09 [Member]
1. Summary of Accounting Policies (Details) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets			109,000
Retained Earnings [Member] | Accounting Standards Update 2014-09 [Member]
1. Summary of Accounting Policies (Details) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets			$ 22,000