Name:	buks_SupplementalTypeCertificatesAccumulatedAmortization
Namespace Prefix:	buks_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Supplemental Type Certificates capitalized before adjustment of amortization.

No definition available.

Name:	buks_SupplementalTypeCertificatesCapitalizedGross
Namespace Prefix:	buks_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Capitalized consultants cost attributable to Supplemental Type Certificates.

No definition available.

Name:	buks_SupplementalTypeCertificatesConsultantCostsCapitalized
Namespace Prefix:	buks_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Capitalized direct labor cost attributable to Supplemental Type Certificates.

No definition available.

Name:	buks_SupplementalTypeCertificatesDirectLaborCapitalized
Namespace Prefix:	buks_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Capitalized direct materials cost attributable to Supplemental Type Certificates.

No definition available.

Name:	buks_SupplementalTypeCertificatesDirectMaterialsCapitalized
Namespace Prefix:	buks_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Capitalized overhead cost attributable to Supplemental Type Certificates.

No definition available.

Name:	buks_SupplementalTypeCertificatesOverheadCapitalized
Namespace Prefix:	buks_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph ((a)(1),(b))
-URI https://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6388964&loc=d3e16212-109274