Fixed assets pledged for secured loan value.

No definition available.

Name:	bgcp_FixedAssetsPledgedForSecuredLoanValue
Namespace Prefix:	bgcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
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-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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+ Details

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

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
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://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 210
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+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
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+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_GuaranteeObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Schedule I - Parent Company Only - Commitments, Contingencies and Guarantees - Additional Information (Detail) - USD ($)			12 Months Ended
	Apr. 19, 2019	Apr. 08, 2019	Dec. 31, 2020	Dec. 31, 2019	May 31, 2017	Jul. 10, 2015	Mar. 13, 2015
3.70% [Member]
Loss Contingencies [Line Items]
Outstanding balance of the secured loan arrangements			$ 0	$ 0
3.70% [Member] \| Secured Loan Arrangements [Member]
Loss Contingencies [Line Items]
Debt instrument gross amount							$ 28,200,000
Stated interest rate							3.70%
Senior Notes maturity date			Mar. 13, 2019
8.375% Senior Notes [Member]
Loss Contingencies [Line Items]
Stated interest rate			8.375%
Principal amount of notes			$ 240,000,000.0
3.44% [Member]
Loss Contingencies [Line Items]
Outstanding balance of the secured loan arrangements			$ 4,000,000.0	11,700,000
3.44% [Member] \| Secured Loan Arrangements [Member]
Loss Contingencies [Line Items]
Debt instrument gross amount					$ 29,900,000
Stated interest rate					3.44%
Senior Notes maturity date			May 31, 2021
Book value of the fixed assets pledged			$ 800,000	2,300,000
3.77% [Member]
Loss Contingencies [Line Items]
Outstanding balance of the secured loan arrangements			9,600,000	13,200,000
3.77% [Member] \| Secured Loan Arrangements [Member]
Loss Contingencies [Line Items]
Debt instrument gross amount		$ 15,000,000.0
Stated interest rate		3.77%
Senior Notes maturity date		Apr. 08, 2023
Book value of the fixed assets pledged			1,200,000	8,100,000
3.89% [Member]
Loss Contingencies [Line Items]
Outstanding balance of the secured loan arrangements			6,300,000	8,800,000
3.89% [Member] \| Secured Loan Arrangements [Member]
Loss Contingencies [Line Items]
Debt instrument gross amount	$ 10,000,000.0
Stated interest rate	3.89%
Senior Notes maturity date	Apr. 19, 2023
Book value of the fixed assets pledged			$ 2,700,000	5,700,000
Parent Company [Member] \| 3.70% [Member] \| Secured Loan Arrangements [Member]
Loss Contingencies [Line Items]
Debt instrument gross amount							$ 28,200,000
Stated interest rate							3.70%
Senior Notes maturity date			Mar. 13, 2019
Line of credit facility, outstanding amount			$ 0	0
Parent Company [Member] \| 8.375% Senior Notes [Member] \| Guarantee Obligations [Member]
Loss Contingencies [Line Items]
Stated interest rate						8.375%
Principal amount of notes						$ 240,000,000.0
Parent Company [Member] \| 3.44% [Member]
Loss Contingencies [Line Items]
Outstanding balance of the secured loan arrangements			$ 4,000,000.0	11,700,000
Parent Company [Member] \| 3.44% [Member] \| Secured Loan Arrangements [Member]
Loss Contingencies [Line Items]
Debt instrument gross amount					$ 29,900,000
Stated interest rate					3.44%
Senior Notes maturity date			May 31, 2021
Book value of the fixed assets pledged			$ 800,000	2,300,000
Parent Company [Member] \| 3.77% [Member]
Loss Contingencies [Line Items]
Outstanding balance of the secured loan arrangements			$ 9,600,000	13,200,000
Parent Company [Member] \| 3.77% [Member] \| Secured Loan Arrangements [Member]
Loss Contingencies [Line Items]
Debt instrument gross amount		$ 15,000,000.0
Stated interest rate		3.77%
Senior Notes maturity date			Apr. 08, 2023
Book value of the fixed assets pledged			$ 1,200,000	8,100,000
Parent Company [Member] \| 3.89% [Member]
Loss Contingencies [Line Items]
Outstanding balance of the secured loan arrangements			6,300,000	8,800,000
Parent Company [Member] \| 3.89% [Member] \| Secured Loan Arrangements [Member]
Loss Contingencies [Line Items]
Debt instrument gross amount	$ 10,000,000.0
Stated interest rate	3.89%
Senior Notes maturity date	Apr. 19, 2023
Book value of the fixed assets pledged			$ 2,700,000	$ 5,700,000