Short term borrowings excluding repurchase agreements.

No definition available.

Name:	bgcp_ShortTermBorrowingsExcludingRepurchaseAgreements
Namespace Prefix:	bgcp_
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

+ Details

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

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Carrying amount of collateralized debt obligations with maturities initially due after one year or beyond the operating cycle, if longer, excluding the current portion. Obligations include, but not limited to, mortgage loans, chattel loans, and other borrowings secured by assets.

+ References

+ Details

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

- Definition

Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

+ Details

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

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=bgcp_FourPointThreeSevenFivePercentageSeniorNotesMember
Namespace Prefix:
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Period Type:

Notes Payable, Other and Short-Term Borrowings - Summary Notes Payable, Other and Short-term Borrowings (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Jul. 10, 2020	Sep. 27, 2019	Jul. 24, 2018	May 27, 2016
Debt Instrument [Line Items]
Carrying amount of Collateralized borrowings	$ 16,330	$ 19,854
Total Notes payable and other borrowings	1,313,295	1,315,935
Short-term borrowings	3,510	3,849
Carrying amount of Total Notes payable, other and short-term borrowings	1,316,805	1,319,784
5.125% Senior Notes [Member]
Debt Instrument [Line Items]
Carrying amount of Senior Notes	255,847	255,570
Carrying amount of Total Notes payable, other and short-term borrowings	255,800					$ 295,800
5.375% Senior Notes [Member]
Debt Instrument [Line Items]
Carrying amount of Senior Notes	446,911	446,577
Carrying amount of Total Notes payable, other and short-term borrowings					$ 444,200
3.750% Senior Notes [Member]
Debt Instrument [Line Items]
Carrying amount of Senior Notes	297,110	296,903
Carrying amount of Total Notes payable, other and short-term borrowings	297,100			$ 296,100
4.375% Senior Notes [Member]
Debt Instrument [Line Items]
Carrying amount of Senior Notes	297,097	$ 297,031
Carrying amount of Total Notes payable, other and short-term borrowings	$ 297,100		$ 296,800