XML 43 R32.htm IDEA: XBRL DOCUMENT
v3.10.0.1

REVENUE, Significant Payment Terms (Details) | 9 Months Ended
--- | ---
Sep. 30, 2018
Significant Payment Terms [Abstract] |
Period of payment for products sold under consignment contracts due from customer pulling the product from the hub | 60 days
Minimum [Member] |
Warranties [Abstract] |
Standard warranty period of product | 1 year
Maximum [Member] |
Warranties [Abstract] |
Standard warranty period of product | 3 years
Direct to Customer [Member] | Minimum [Member] |
Significant Payment Terms [Abstract] |
Period of payment for products sold due | 30 days
Direct to Customer [Member] | Maximum [Member] |
Significant Payment Terms [Abstract] |
Period of payment for products sold due | 90 days
Through Distribution [Member] | Minimum [Member] |
Significant Payment Terms [Abstract] |
Period of payment for products sold due | 30 days
Through Distribution [Member] | Maximum [Member] |
Significant Payment Terms [Abstract] |
Period of payment for products sold due | 90 days
Power Solutions and Protection [Member] | Maximum [Member] |
Licensing Agreements [Abstract] |
Payment received on reporting date, quarterly or annual | 30 days

X
- References No definition available. + Details
Name: | belfb_LicensingAgreementsAbstract
Namespace Prefix: | belfb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The payment for products sold under direct contracts with customers or contracts with distributors is typically due in full within mentioned days from the transfer of title to customer + References No definition available. + Details
Name: | belfb_PeriodOfPaymentForProductsSoldDue
Namespace Prefix: | belfb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period of payment for products sold under consignment contracts due of the customer pulling the product from the hub. + References No definition available. + Details
Name: | belfb_PeriodOfPaymentForProductsSoldUnderConsignmentContractsDueFromCustomerPullingTheProductFromHub
Namespace Prefix: | belfb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The Income related to these agreements is tracked by the licensee throughout the year based on their sales of product that utilize, and that data is reported either on a quarterly or annual basis, with payment generally received within the reporting date. + References No definition available. + Details
Name: | belfb_PeriodOfPaymentReceivedOnReportingDateQuarterlyOrAnnual
Namespace Prefix: | belfb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | belfb_SignificantPaymentTermsAbstract
Namespace Prefix: | belfb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents standard warranty period in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | belfb_StandardWarrantyPeriodOfProduct
Namespace Prefix: | belfb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_ProductWarrantiesDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ContractWithCustomerSalesChannelAxis=us-gaap_SalesChannelDirectlyToConsumerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ContractWithCustomerSalesChannelAxis=us-gaap_SalesChannelThroughIntermediaryMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=belfb_PowerSolutionsAndProtectionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |