Note 15 - Segment Reporting and Sales by Major Customer - Schedule of Revenue by Major Customers by Reporting Segments (Details) (Parentheticals)	6 Months Ended
Oct. 31, 2022	Oct. 31, 2021
Revenue Benchmark [Member] \| Customer Concentration Risk [Member] \| Aerospace Products [Member]
Number of customers	2	2

Represents information about number of major customers.

No definition available.

Name:	buks_NumberOfMajorCustomers
Namespace Prefix:	buks_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration