Note 2 - Debt - Schedule of Debt (Details) (Parentheticals) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016
Note Payable Paid off in 2017 [Member]
Interest rate	6.00%	6.00%
Debt Instrument Due December 2017 and March 2018 [Member]
Maturity date range, start	Dec. 31, 2017	Dec. 31, 2016
Maturity date range, end	Mar. 31, 2018	Mar. 31, 2018
Note Collateralized by Real Estate [Member]
Borrowing capacity	$ 5	$ 5
Basis spread	3.40%	3.40%
Note Collateralized by Real Estate [Member] | Note Payable Due August 2019 [Member]
Maturity date	Aug. 31, 2019
Note Collateralized by Real Estate [Member] | Note Payable Due August 2019 [Member] | Prime Rate [Member]
Interest rate	3.36%
Note Collateralized by Real Estate [Member] | Note 1 Due March 2019 [Member]
Maturity date	Mar. 31, 2019
Note Collateralized by Real Estate [Member] | Note 1 Due March 2019 [Member] | Prime Rate [Member]
Interest rate	3.36%
Note Collateralized by Real Estate [Member] | Note 2 Due March 2019 [Member]
Maturity date	Mar. 31, 2019
Note Collateralized by Real Estate [Member] | Note 2 Due March 2019 [Member] | Prime Rate [Member]
Interest rate	2.68%
Note Collateralized by Real Estate [Member] | Note Payable Due June 2016 [Member]
Interest rate	6.25%	6.25%
Maturity date	Jun. 30, 2019	Jun. 30, 2019
Notes Collateralized by Aircraft Security Agreements [Member] | Note Payable Due September 2017 [Member]
Interest rate	6.25%	6.25%
Maturity date	Sep. 30, 2017	Sep. 30, 2017
Notes Collateralized by Aircraft Security Agreements [Member] | Debt Instrument Due January 2020 [Member]
Interest rate	5.75%	5.75%
Maturity date	Jan. 31, 2020	Jan. 31, 2020
Note Collateralized by BNSC's Assets and Compensation due under State Management Contract [Member] | Debt Instrument Due May 2020 [Member]
Interest rate	4.89%	4.89%
Maturity date	May 31, 2020	May 31, 2020
Note Collateralized by Equipment [Member] | Note Payable Due April 2020 [Member]
Interest rate	4.50%	4.50%
Maturity date	Apr. 30, 2022	Apr. 30, 2022