XML 25 R55.htm IDEA: XBRL DOCUMENT
v3.20.1

Note 4 - Goodwill and Other Intangible Assets - Estimated Fair Values Over Carrying Value, Including Goodwill (Details) - Europe [Member] | Dec. 31, 2019 | Sep. 30, 2019
--- | --- | ---
% by Which Estimated Fair Value Exceeds Carrying Value |  | 17.30%
Cinch Connectivity Solutions Segment [Member] |  |
% by Which Estimated Fair Value Exceeds Carrying Value | 138.80% |
Power Solutions and Protection Segment [Member] |  |
% by Which Estimated Fair Value Exceeds Carrying Value | 16.40% |

X
- Definition Percentage of fair value of reporting unit in excess of carrying amount. + References No definition available. + Details
Name: | us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | srt_StatementGeographicalAxis=srt_EuropeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=belfa_CinchConnectivitySolutionsSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=belfa_PowerSolutionsAndProtectionSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |