Note 2 - Debt - Schedule of Debt (Details) (Parentheticals) - USD ($) $ in Millions	12 Months Ended
Apr. 30, 2019	Apr. 30, 2018
Notes Collateralized by Aircraft Security Agreements, Due January 2020 [Member]
Interest rate	5.75%	5.75%
Maturity date	Jan. 31, 2020	Jan. 31, 2020
Notes Collateralized by Aircraft Security Agreements, Due January 2023 [Member]
Interest rate	6.25%	6.25%
Maturity date	Jan. 31, 2023	Jan. 31, 2023
Note Collateralized by Real Estate Due June 2024 [Member]
Interest rate	6.25%	6.25%
Maturity date	Jun. 30, 2024	Jun. 30, 2024
Note Collateralized by BNSC's Assets and Compensation due under State Management Contract Due May 2020 [Member]
Interest rate	4.89%	4.89%
Maturity date	May 31, 2020	May 31, 2020
Note Collateralized by Equipment Due April 2022 [Member]
Interest rate	4.50%	4.50%
Maturity date	Apr. 30, 2022	Apr. 30, 2022
Note Collateralized by Real Estate [Member]
Borrowing capacity	$ 5	$ 5
Basis spread	3.40%	3.40%

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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