Cash tender offer amount.

No definition available.

Name:	bgcp_CashTenderOfferAmount
Namespace Prefix:	bgcp_
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

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

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ 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
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

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

- 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

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

+ References

No definition available.

+ Details

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

- Definition

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28555-108399

+ Details

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

- Definition

Date the declared dividend will be paid, in CCYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The per share amount of a dividend declared, but not paid, as of the financial reporting date.

+ References

+ Details

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

- Definition

Date the dividend to be paid was declared, in CCYY-MM-DD format.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
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-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

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

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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Period Type:	duration

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Subsequent Events - Additional Information (Detail) - USD ($)				6 Months Ended
	Jul. 29, 2020	Jul. 14, 2020	Jul. 10, 2020	Jun. 30, 2020	Aug. 05, 2020	Dec. 31, 2019	May 27, 2016
Subsequent Event [Line Items]
Carrying amount of debt component				$ 1,294,625,000		$ 1,147,649,000
4.375% Senior Notes [Member]
Subsequent Event [Line Items]
Debt instrument, periodic interest payment description				The notes will pay interest semi-annually at a rate of 4.375% per annum, on each June 15 and December 15, beginning on December 15, 2020
5.125% Senior Notes [Member]
Subsequent Event [Line Items]
Principal amount of notes				$ 300,000,000.0			$ 300,000,000.0
Stated interest rate				5.125%		5.125%
Debt instrument, periodic interest payment description				payable in cash on May 27 and November 27 of each year, commencing November 27, 2016
Senior Notes maturity date				May 27, 2021
Carrying amount of debt component				$ 299,100,000			295,800,000
Debt issuance costs							4,200,000
Principal amount of debt component				$ 300,000,000.0			$ 300,000,000.0
Subsequent Event [Member] \| Senior Revolving Credit Agreement [Member]
Subsequent Event [Line Items]
Repayment of borrowings outstanding		$ 225,000,000.0
Subsequent Event [Member] \| 4.375% Senior Notes [Member]
Subsequent Event [Line Items]
Principal amount of notes			$ 300,000,000.0
Stated interest rate			4.375%
Senior Notes maturity date			Dec. 15, 2025
Carrying amount of debt component			$ 296,800,000
Debt issuance costs			3,200,000
Principal amount of debt component			$ 300,000,000.0
Subsequent Event [Member] \| 5.125% Senior Notes [Member]
Subsequent Event [Line Items]
Stated interest rate					5.125%
Cash tender offer amount					$ 300,000,000
Class A Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared per share	$ 0.01
Dividend payable declared date	Jul. 29, 2020
Dividend payable, date to be paid	Sep. 02, 2020
Dividend payable record date	Aug. 19, 2020
Class B Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared per share	$ 0.01
Dividend payable declared date	Jul. 29, 2020
Dividend payable, date to be paid	Sep. 02, 2020
Dividend payable record date	Aug. 19, 2020