Note 15 - Concentration (Details Textual) - USD ($)	3 Months Ended	9 Months Ended
Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Revenue from Contract with Customer, Including Assessed Tax	$ 9,052,000	$ 9,094,000	$ 27,074,000	$ 26,997,000
Customer Concentration Risk [Member] \| Sales Revenue, Net [Member] \| One Single Customer [Member]
Concentration Risk, Percentage			19.60%
Revenue from Contract with Customer, Including Assessed Tax			$ 27,074,000

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
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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
-Name Accounting Standards Codification
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

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