Compensation - Limited Partnership Units with a Post-Termination Payout (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
BGC Holdings, L.P.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Notional value	$ 261,025	$ 223,665
Estimated fair value of the post-termination payout	$ 58,149	$ 30,655
Outstanding limited partnership units (in shares)	6,251,816	8,443,218
Outstanding limited partnership units - unvested (in dollars per share)	1,508,510	3,256,894
NEWMARK Group Inc Parent
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding limited partnership units (in shares)	17,097,639	10,520,196
Outstanding limited partnership units - unvested (in dollars per share)	9,357,822	6,820,930

Notional value of limited partnership units with post termination pay out amount.

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options outstanding grant date fair value.

+ References

No definition available.

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- Definition

The number of limited partner units outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- 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.

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