Description Of Business [Line Items]

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- Definition

Economic interest ownership percentage.

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No definition available.

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- Definition

Limited partnership units exchange ratio.

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No definition available.

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- Definition

Number of units converted to common stock.

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No definition available.

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- Definition

Shares Acquired In Spin-off

+ References

No definition available.

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- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ 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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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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- Definition

Number of common units issued of limited liability company (LLC).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
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-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

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- Definition

Balance held at close of period in number of shares.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=120401592&loc=d3e611197-123010

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- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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No definition available.

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- Definition

The cash outflow associated with the acquisition of or advances to an entity that is related to it but not strictly controlled (for example, an unconsolidated subsidiary, affiliate, and joint venture or equity method investment) or the acquisition of an additional interest in a subsidiary (controlled entity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
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-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

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Schedule I - Parent Company Only - Organization and Basis of Presentation (Detail) $ in Millions	Nov. 30, 2018 shares	Mar. 07, 2018 USD ($) shares	Dec. 31, 2020 shares	Nov. 30, 2020 shares	Dec. 31, 2019 shares	Dec. 02, 2019 shares	Nov. 29, 2018 shares	Dec. 13, 2017
Description Of Business
Shares owned (in shares)				250,742		93,562
Common Class A
Description Of Business
Limited partnership units exchange ratio (in percentage)								1
Common stock, shares issued (in shares)			167,604,348		160,833,463
Common Class B
Description Of Business
Common stock, shares issued (in shares)			21,285,533		21,285,533
NEWMARK Group Inc Parent
Description Of Business
Common stock units issued (in shares)	1,458,931
NEWMARK Group Inc Parent \| BGC Partners LP and its Operating Subsidiaries \| Newmark Units
Description Of Business
Purchase of units (units)		16,600,000
Purchase value of units \| $		$ 242.0
NEWMARK Group Inc Parent \| Common Class A
Description Of Business
Limited partnership units exchange ratio (in percentage)			0.9379
Common stock units issued (in shares)	449,917
NEWMARK Group Inc Parent \| Spinoff \| Newmark Holdings \| BGC Partners Inc
Description Of Business
Shares owned (in shares)							14,800,000
NEWMARK Group Inc Parent \| Spinoff \| Common Class A
Description Of Business
Limited partnership units exchange ratio (in percentage)	0.463895
Number of units converted to common stock (in shares)	9,400,000
NEWMARK Group Inc Parent \| Spinoff \| Common Class A \| Newmark OpCo
Description Of Business
Number of units converted to common stock (in shares)	6,900,000
NEWMARK Group Inc Parent \| Spinoff \| Common Class A \| Newmark Group \| BGC Partners Inc
Description Of Business
Common stock, shares issued (in shares)	131,886,409
Ownership interest (percentage)	94.00%
Economic interest ownership percentage (in percentage)	87.00%
NEWMARK Group Inc Parent \| Spinoff \| Common Class B
Description Of Business
Limited partnership units exchange ratio (in percentage)	0.463895
Number of units converted to common stock (in shares)	5,400,000
NEWMARK Group Inc Parent \| Spinoff \| Common Class B \| Newmark Group \| BGC Partners Inc
Description Of Business
Common stock, shares issued (in shares)	21,285,537
NEWMARK Group Inc Parent \| Spinoff \| Common Stock \| Newmark OpCo
Description Of Business
Number of units converted to common stock (in shares)	7,000,000.0