2. Summary of Significant Accounting Policies (Details Narrative) - USD ($) $ in Thousands	12 Months Ended
Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Restricted cash pledged as collateral	$ 1,150	$ 1,150	$ 1,150
Revenue recognized for which the contract liability was recorded in the prior year	14,312
Allowance for doubtful accounts	0	0
Interest expense on construction in progress	0
Depreciation and amortization	2,746	2,562	$ 2,463
Impairment of long-lived assets	0	$ 0
Cumulative effect of ASC 606 adoption	$ 2,739
Sales Revenue Net [Member]
Concentration risk percentage	95.00%	99.00%	100.00%

Amount of allowance for credit loss on accounts receivable.

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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.

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Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount of cash restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

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