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Accounts Payable and Accrued Liabilities - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016
Statement of Financial Position [Abstract] |  |
Accounts payable due to bank | $ 21.9 | $ 12.4
Settlement of accounts payable outstanding | 1 year |

X
- Definition Accounts payable due to bank current. + References No definition available. + Details
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Namespace Prefix: | bdc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Term of settlement of accounts payable due to bank. + References No definition available. + Details
Name: | bdc_TermOfSettlementOfAccountsPayableDueToBank
Namespace Prefix: | bdc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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