Senior Secured Credit Facility Restrictive Covenants, Fixed Charge Coverage Ratio Minimum Threshold

No definition available.

Name:	bdc_SeniorSecuredCreditFacilityRestrictiveCovenantsFixedChargeCoverageRatioMinimumThreshold
Namespace Prefix:	bdc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13476-108611

+ Details

Name:	us-gaap_DebtInstrumentFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of the fee that accompanies borrowing money under the debt instrument.

+ References

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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

- 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

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

- Definition

Fair value amount of debt instrument that was repurchased.

+ References

No definition available.

+ Details

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

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=49170532&loc=d3e12317-112629

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=49170532&loc=d3e12355-112629

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

+ Details

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

- Definition

Carrying value as of the balance sheet date of collateralized/uncollateralized debt obligation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Subordinated debt places a lender in a lien position behind the primary lender of the company.

+ References

+ Details

Name:	us-gaap_SubordinatedLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorSubordinatedNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bdc_RevolvingCreditFacilityMatureTwoThousandTwentyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bdc_A3.875SeniorSubordinatedNotesDue2028Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bdc_A3.375SeniorSubordinatedNotesDue2027Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bdc_A4.125SeniorSubordinatedNotesDue2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bdc_A2.875SeniorSubordinatedNotesDue2025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bdc_FivePointTwoFivePercentSeniorSubordinatedNotesDueTwoThousandTwentyFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bdc_FivePointFiveZeroPercentSeniorSubordinatedNotesDueTwoThousandTwentyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt and Other Borrowing Arrangements - Additional Information (Detail)		1 Months Ended		3 Months Ended
	May 16, 2017 USD ($)	Mar. 31, 2018 EUR (€)	Mar. 31, 2018 USD ($)	Apr. 01, 2018 USD ($)	Apr. 02, 2017 USD ($)	Apr. 01, 2018 EUR (€)	Apr. 01, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Senior subordinated notes							$ 1,687,903,000		$ 1,584,232,000
Loss on debt extinguishment				$ 19,960,000	$ 0
Senior Subordinated Notes
Debt Instrument [Line Items]
Fair value of debt instrument							1,685,800,000
Revolving credit agreement due 2022
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 400,000,000
Commitment fee percentage	0.25%
Fixed charge coverage, minimum threshold (as a percent)	90.00%
Borrowings outstanding							0		$ 0
Available borrowing capacity							$ 333,400,000
Revolving credit agreement due 2022 \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (as a percent)	1.25%
Revolving credit agreement due 2022 \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (as a percent)	1.75%
3.875% Senior subordinated notes due 2028
Debt Instrument [Line Items]
Senior subordinated notes interest rate						3.875%	3.875%		3.875%
Senior subordinated notes							$ 432,320,000		$ 0
3.875% Senior subordinated notes due 2028 \| Senior Subordinated Notes
Debt Instrument [Line Items]
Aggregate principal amount outstanding of senior subordinated notes		€ 350,000,000.0						$ 431,300,000
Senior subordinated notes interest rate		3.875%						3.875%
Fees incurred to creditors and third parties								$ 7,100,000
3.375% Senior subordinated notes due 2027
Debt Instrument [Line Items]
Senior subordinated notes interest rate						3.375%	3.375%		3.375%
Senior subordinated notes							$ 555,840,000		$ 540,810,000
3.375% Senior subordinated notes due 2027 \| Senior Subordinated Notes
Debt Instrument [Line Items]
Aggregate principal amount outstanding of senior subordinated notes \| €						€ 450,000,000
Senior subordinated notes interest rate						3.375%	3.375%
4.125% Senior subordinated notes due 2026
Debt Instrument [Line Items]
Senior subordinated notes interest rate						4.125%	4.125%		4.125%
Senior subordinated notes							$ 247,040,000		$ 240,360,000
4.125% Senior subordinated notes due 2026 \| Senior Subordinated Notes
Debt Instrument [Line Items]
Aggregate principal amount outstanding of senior subordinated notes \| €						€ 200,000,000
2.875% Senior subordinated notes due 2025
Debt Instrument [Line Items]
Senior subordinated notes interest rate						2.875%	2.875%		2.875%
Senior subordinated notes							$ 370,560,000		$ 360,540,000
2.875% Senior subordinated notes due 2025 \| Senior Subordinated Notes
Debt Instrument [Line Items]
Aggregate principal amount outstanding of senior subordinated notes \| €						€ 300,000,000
Senior subordinated notes interest rate						2.875%	2.875%
Fair value of debt instrument							$ 370,600,000
5.25% Senior subordinated notes due 2024
Debt Instrument [Line Items]
Senior subordinated notes interest rate						5.25%	5.25%		5.25%
Senior subordinated notes							$ 11,291,000		$ 200,000,000
5.25% Senior subordinated notes due 2024 \| Senior Subordinated Notes
Debt Instrument [Line Items]
Aggregate principal amount outstanding of senior subordinated notes							$ 200,000,000.0
Senior subordinated notes interest rate						5.25%	5.25%
Senior subordinated notes							$ 11,300,000
Debt repurchased								$ 188,700,000
Repayments of debt			$ 199,800,000
Loss on debt extinguishment			(13,800,000)
5.50% Senior subordinated notes due 2023
Debt Instrument [Line Items]
Senior subordinated notes interest rate						5.50%	5.50%		5.50%
Senior subordinated notes							$ 70,852,000		$ 242,522,000
5.50% Senior subordinated notes due 2023 \| Senior Subordinated Notes
Debt Instrument [Line Items]
Aggregate principal amount outstanding of senior subordinated notes \| €						€ 200,000,000.0
Senior subordinated notes interest rate						5.50%	5.50%
Debt repurchased \| €		€ 143,100,000
Repayments of debt		€ 147,800,000	182,100,000
Loss on debt extinguishment			$ (6,200,000)