Compensation - Activity Associated with Limited Partnership Units (Details) - shares	9 Months Ended	12 Months Ended
Sep. 30, 2025	Dec. 31, 2024
Newmark Holdings Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	51,796,454	42,376,966
Number of units, Issued (in shares)	8,312,058	16,440,711
Number of units, Redeemed/exchanged units (in shares)	(8,633,144)	(6,166,506)
Number of units, Forfeited units/other (in shares)	(598,722)	(854,717)
Ending balance (in shares)	50,876,646	51,796,454
Exchangeable units (in shares)	13,979,506	13,906,798
Newmark Holdings Units \| Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	2,700,000
Ending balance (in shares)	2,500,000	2,700,000
Exchangeable partnership units (in shares)	1,700,000	1,800,000
Newmark Holdings Units \| Limited Partnership Units \| Employee
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	2,200,000
BGC Holdings Units \| Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	0

Exchangeable Partnership Units

No definition available.

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- Definition

Exchangeable Units

+ References

No definition available.

+ Details

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- Definition

Number of exchangeable limited partnership units redeemed or exchanged into the Company's class A common stock during the period.

+ References

No definition available.

+ Details

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- Definition

Number of shares under non-option equity instrument agreements that were cancelled as a result of occurrence of a terminating event.

+ References

+ Details

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- Definition

Net number of non-option equity instruments granted to participants.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(01)
-SubTopic 10
-Topic 718
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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- 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

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