Organization and Significant Accounting Policies - Concentration of Credit Risk (Details)	12 Months Ended
Apr. 30, 2022	Apr. 30, 2021	Apr. 30, 2020
Customer concentration \| Sales Revenue \| US Government Agencies
Concentration of Credit Risk
Concentration Risk, Percentage	66.00%	69.00%	61.00%
Customer concentration \| Sales Revenue \| US Army
Concentration of Credit Risk
Concentration Risk, Percentage	21.00%	34.00%	32.00%
Credit concentration \| Accounts receivable balances \| US Government Agencies
Concentration of Credit Risk
Concentration Risk, Percentage	65.00%	64.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13531-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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