Pension and Other Postretirement Benefits - Benefits Expected to be Paid in Subsequent Years from Our Pension and Other Postretirement as Well as Medicare Subsidy Receipts (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Medicare Subsidy Receipts [Member]
Pension And Other Employee Benefit Plans [Line Items]
2015	$ 91
2016	84
2017	77
2018	70
2019	63
2020-2024	214
Total	599
Pension Benefits [Member]
Pension And Other Employee Benefit Plans [Line Items]
2015	16,323
2016	17,346
2017	17,969
2018	18,357
2019	18,292
2020-2024	94,607
Total	182,894
Other Benefits [Member]
Pension And Other Employee Benefit Plans [Line Items]
2015	2,328
2016	2,283
2017	2,238
2018	2,167
2019	2,080
2020-2024	9,805
Total	$ 20,901

Pension and Other Postretirement Benefits - Benefits Expected to be Paid in Subsequent Years from Our Pension and Other Postretirement as Well as Medicare Subsidy Receipts (Detail) (USD $)
In Thousands, unless otherwise specified

Dec. 31, 2014

$ 91us-gaap_PrescriptionDrugSubsidyReceiptsNextTwelveMonths
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_MedicareSubsidyBenefitsMember

84us-gaap_PrescriptionDrugSubsidyReceiptsYearTwo1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_MedicareSubsidyBenefitsMember

2017

77us-gaap_PrescriptionDrugSubsidyReceiptsYearThree1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_MedicareSubsidyBenefitsMember

2018

70us-gaap_PrescriptionDrugSubsidyReceiptsYearFour1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_MedicareSubsidyBenefitsMember

2019

63us-gaap_PrescriptionDrugSubsidyReceiptsYearFive1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_MedicareSubsidyBenefitsMember

2020-2024

214us-gaap_PrescriptionDrugSubsidyReceiptsAfterYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_MedicareSubsidyBenefitsMember

Total

599bdc_PrescriptionDrugSubsidyReceiptsNextTenYears
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_MedicareSubsidyBenefitsMember

Pension Benefits [Member]

Pension And Other Employee Benefit Plans [Line Items]

2015

16,323us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_PensionBenefitsMember

2016

17,346us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_PensionBenefitsMember

2017

17,969us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_PensionBenefitsMember

2018

18,357us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_PensionBenefitsMember

2019

18,292us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_PensionBenefitsMember

2020-2024

94,607us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_PensionBenefitsMember

Total

182,894bdc_DefinedBenefitPlanExpectedFutureBenefitPaymentsInNextTenYears
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_PensionBenefitsMember

Other Benefits [Member]

Pension And Other Employee Benefit Plans [Line Items]

2015

2,328us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_OtherBenefitsMember

2016

2,283us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_OtherBenefitsMember

2017

2,238us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_OtherBenefitsMember

2018

2,167us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_OtherBenefitsMember

2019

2,080us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_OtherBenefitsMember

2020-2024

9,805us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_OtherBenefitsMember

Total

$ 20,901bdc_DefinedBenefitPlanExpectedFutureBenefitPaymentsInNextTenYears
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= bdc_OtherBenefitsMember

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- Definition

Prescription Drug Subsidy Receipts Next Ten Years

+ References

No definition available.

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of the prescription drug subsidy receipts to be received after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 60

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964

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- Definition

Amount of the prescription drug subsidy receipts to be received in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of the prescription drug subsidy receipts to be received in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of the prescription drug subsidy receipts to be received in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of the prescription drug subsidy receipts to be received in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of the prescription drug subsidy receipts to be received in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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