Noncontrolling Interest - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity, Primary Beneficiary [Member]
Noncontrolling Interest [Line Items]
Contribution to joint venture		$ 1,530
Additional contribution commitments to joint venture	$ 1,530
Hite [Member]
Noncontrolling Interest [Line Items]
Contribution to joint venture		$ 1,470
Ownership percentage		49.00%
Additional contribution commitments to joint venture	$ 1,470
Hite [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Noncontrolling Interest [Line Items]
Variable interest entity, ownership percentage		51.00%

Additional contribution commitments to joint venture.

No definition available.

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Namespace Prefix:	bdc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow associated with the investment in or advances to an entity in which the reporting entity shares control of the entity with another party or group.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3213-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=bdc_HiteMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: