Intangible Assets - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 1,385,995	$ 1,385,115
Acquisitions and purchase accounting adjustments	71,394	8,492
Translation impact	20,868	(2,135)
Reclassify to assets held for sale		(5,477)
Goodwill, Ending Balance	1,478,257	1,385,995
Broadcast Solutions [Member]
Goodwill [Roll Forward]
Goodwill, Beginning Balance	544,042	536,388
Acquisitions and purchase accounting adjustments	71,394	8,492
Translation impact	13,557	(838)
Reclassify to assets held for sale		0
Goodwill, Ending Balance	628,993	544,042
Enterprise Solutions [Member]
Goodwill [Roll Forward]
Goodwill, Beginning Balance	73,278	73,278
Acquisitions and purchase accounting adjustments	0	0
Translation impact	0	0
Reclassify to assets held for sale		0
Goodwill, Ending Balance	73,278	73,278
Industrial Solutions [Member]
Goodwill [Roll Forward]
Goodwill, Beginning Balance	191,322	196,719
Acquisitions and purchase accounting adjustments	0	0
Translation impact	2,790	80
Reclassify to assets held for sale		(5,477)
Goodwill, Ending Balance	194,112	191,322
Network Solutions [Member]
Goodwill [Roll Forward]
Goodwill, Beginning Balance	577,353	578,730
Acquisitions and purchase accounting adjustments	0	0
Translation impact	4,521	(1,377)
Reclassify to assets held for sale		0
Goodwill, Ending Balance	$ 581,874	$ 577,353

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

+ Details

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

+ Details

Name:	us-gaap_GoodwillAcquiredDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

+ Details

Name:	us-gaap_GoodwillForeignCurrencyTranslationGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_GoodwillRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

+ Details

Name:	us-gaap_GoodwillWrittenOffRelatedToSaleOfBusinessUnit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=bdc_BroadcastSolutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=bdc_EnterpriseSolutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=bdc_IndustrialSolutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=bdc_NetworkSolutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: