Related Party Transactions - Transactions With Executive Officers and Directors (Details)								1 Months Ended			3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 29, 2022 shares	Apr. 14, 2022 USD ($) $ / shares shares	Dec. 21, 2021 USD ($) $ / shares shares	Sep. 20, 2021 USD ($) shares	Jun. 28, 2021 USD ($) $ / shares shares	Apr. 27, 2021 USD ($) $ / shares shares	Mar. 16, 2021 USD ($) $ / shares shares	Sep. 30, 2022 $ / shares shares	Aug. 31, 2022 $ / shares shares	Jul. 31, 2022 $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Jun. 30, 2022 $ / shares shares	Mar. 31, 2022 $ / shares shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) shares	Dec. 31, 2021 USD ($)	Dec. 13, 2017
Related Party Transaction
Fees to related parties | $											$ 7,301,000			$ 5,664,000	$ 20,878,000	$ 17,696,000
Cantor purchase of Cantor units from Newmark Holdings upon redemption/ exchange of FPU's | $											$ 0				$ 863,000	$ 4,025,000
Related party transaction, award payment term															3 years
Limited partnership units exchange ratio								0.4545			0.4545				0.4545
Class A Common Stock
Related Party Transaction
Treasury stock repurchases (in shares)								4,436,461	3,337,037	2,390,179	10,163,677	11,370,647	1,682,871	6,307,802	23,217,195	10,800,143
Shares repurchased price (in dollars per share) | $ / shares								$ 10.20	$ 10.68	$ 10.19	$ 10.36	$ 12.75	$ 18.35		$ 12.10
Limited partnership units exchange ratio																		1
Michael J. Rispoli
Related Party Transaction
Value of LPU issued in exchange | $							$ 100,000
Michael J. Rispoli | Preferred Units
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)							6,043
Number of share issued for non exchangeable PPSU (in shares)							4,907
Payment of withholding tax rate for common stock issue | $							$ 100,000
Determination price (in dollars per share) | $ / shares							$ 15.57
Michael J. Rispoli | BGC Partners Inc
Related Party Transaction
Cash payment to redeem non exchangeable shares | $					$ 60,750
Michael J. Rispoli | Class A Common Stock
Related Party Transaction
Cash payment to redeem non exchangeable shares | $					$ 52,309
Issuance of Class A common stock for Newmark RSUs (in shares)					21,744
Share price (in dollars per share) | $ / shares							$ 11.09
PSU conversion ratio							0.9365
Limited partnership units exchange ratio					0.9403
Cash payment to redeem | $					$ 60,750
Michael J. Rispoli | Class A Common Stock | BGC Partners Inc
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)					383
Cash payment to redeem | $					$ 134,573
Number of exchangeable (in shares)					36,985
Mr. Gosin
Related Party Transaction
Related party transaction, amounts of transaction | $			$ 15,697,309
Preferred stock, tax rate used in transaction, percent			53.13%
PSU conversion ratio							0.9365
Value of LPU issued in exchange | $							$ 5,800,000
Mr. Gosin | BGC Partners Inc
Related Party Transaction
Cash payment to redeem non exchangeable shares | $					$ 1,129,499
Mr. Gosin | Class A Common Stock
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)							178,232
Issuance of Class A common stock for Newmark RSUs (in shares)			446,711		1,439,658
Shares issued (in dollars per share) | $ / shares			$ 16.47
Related party transaction, shares issued, exchange ratio			93.39%
Share price (in dollars per share) | $ / shares							$ 11.09
Limited partnership units exchange ratio					0.9403
Cash payment to redeem | $					$ 834,508
Mr. Gosin | Class A Common Stock | Newmark Units
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)							82,680
Mr. Gosin | Class A Common Stock | BGC Partners Inc
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)					12,500
Cash payment to redeem | $					$ 298,273
Number of exchangeable (in shares)					3,348,706
Howard W. Lutnick
Related Party Transaction
Related party transaction, amounts of transaction | $			$ 10,340,015
Preferred stock, tax rate used in transaction, percent			57.38%
Cantor purchase of Cantor units from Newmark Holdings upon redemption/ exchange of FPU's | $							$ 21,600,000
Aggregate cash payments | $																	$ 50,000,000
Cash payment to redeem | $					$ 8,798,546
Number of non exchangeable PSU converted (in shares)					2,909,819
Howard W. Lutnick | Related Party Payment, Within Three Days Of Effective Date
Related Party Transaction
Aggregate cash payments | $																	20,000,000
Howard W. Lutnick | Related Party Payment, Within Thirty Days Following Vesting On First Three Anniversaries
Related Party Transaction
Aggregate cash payments | $																	$ 10,000,000
Howard W. Lutnick | BGC Partners Inc
Related Party Transaction
Cash payment to redeem | $					$ 7,983,000
Number of non exchangeable PSU converted (in shares)					1,131,774
Howard W. Lutnick | Class A Common Stock
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)					2,736,103
Issuance of Class A common stock for Newmark RSUs (in shares)			267,572		263,025	5,154
Shares issued (in dollars per share) | $ / shares			$ 16.47
Related party transaction, shares issued, exchange ratio			93.39%
Shares repurchased price (in dollars per share) | $ / shares						$ 10.67
Limited partnership units exchange ratio					0.9403
Cash payment to redeem | $					$ 1,465,874
Howard W. Lutnick | Class A Common Stock | BGC Partners Inc
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)					88,636
Executive Officer | Class A Common Stock
Related Party Transaction
Share price (in dollars per share) | $ / shares					$ 12.50
Executive Officer | Class A Common Stock | BGC Partners Inc
Related Party Transaction
Share price (in dollars per share) | $ / shares					5.86
Executive Officer | Class A Common Stock | Nasdaq
Related Party Transaction
Share price (in dollars per share) | $ / shares					$ 177.11
Mr. Merkel
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)							30,926
Number of share issued for non exchangeable PPSU (in shares)						86,649
Payment of withholding tax rate for common stock issue | $						$ 800,000	$ 300,000
Shares repurchased price (in dollars per share) | $ / shares						$ 10.67
Mr. Merkel | Class A Common Stock
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)							28,962
Share price (in dollars per share) | $ / shares							$ 11.09
Treasury stock repurchases (in shares)						68,727
Stephen M. Merkel | Class A Common Stock
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)					48,072
Limited partnership units exchange ratio					0.9403
Restricted Stock Units | Class A Common Stock
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)											297,266			254,735	1,686,307	1,498,343
Restricted Stock Units | Michael J. Rispoli
Related Party Transaction
Number of conversion rights granted (in shares)	500,000
Restricted Stock Units | Michael J. Rispoli | Tranche One
Related Party Transaction
Number of conversion rights granted (in shares)	100,000
Award vesting period	7 years
Restricted Stock Units | Michael J. Rispoli | Tranche Two
Related Party Transaction
Number of conversion rights granted (in shares)	250,000
Restricted Stock Units | Michael J. Rispoli | Tranche Three
Related Party Transaction
Number of conversion rights granted (in shares)	50,000
Award vesting period	7 years
PSU | Michael J. Rispoli
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)	20,221
Number of exchangeable (in shares)					23,124
PSU | Mr. Gosin
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)							526,828
Number of exchangeable (in shares)					1,438,597.37
PSU | Mr. Gosin | BGC Partners Inc
Related Party Transaction
Number of exchangeable (in shares)					3,147,085
PSU | Howard W. Lutnick
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)					279,725
Issuance of Class A common stock for Newmark RSUs (in shares)							4,423,457
PSU | Howard W. Lutnick | BGC Partners Inc
Related Party Transaction
Number of exchangeable (in shares)					520,380
PSU | Howard W. Lutnick | Class A Common Stock | BGC Partners Inc
Related Party Transaction
Number of exchangeable (in shares)					520,380
PSU | Mr. Merkel
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)						73,387
PSU | Stephen M. Merkel
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)					51,124.28
Non Exchangeable PPSU | Mr. Gosin
Related Party Transaction
Stock redeemed or called during period (in shares)			838,996
Cash payment to redeem non exchangeable shares | $			$ 8,339,980
Fees to related parties | $			$ 7,357,329
Non Exchangeable PPSU | Mr. Gosin | BGC Partners Inc
Related Party Transaction
Number of exchangeable PSU redeemed (in shares)				2,114,546
Non Exchangeable PPSU | Howard W. Lutnick
Related Party Transaction
Stock redeemed or called during period (in shares)			188,883
Stock redeemed or called during period, value | $			$ 1,954,728
Issuance of Class A common stock for Newmark RSUs (in shares)							1,770,016
Non Exchangeable PPSU | Howard W. Lutnick | BGC Partners Inc
Related Party Transaction
Cash payment to redeem | $					$ 1,525,705
Non Exchangeable PPSU | Mr. Merkel
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)						19,426
Payment of withholding tax rate for common stock issue | $						$ 200,000
Non Exchangeable PPSU | Stephen M. Merkel
Related Party Transaction
Cash payment to redeem non exchangeable shares | $					$ 300,000
Number of non exchangeable PPSU redeemed (in shares)					46,349.87
Non Exchangeable PSU | Michael J. Rispoli
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)					6,000
Number of non exchangeable PSU converted (in shares)					5,846.07
Non Exchangeable PSU | Mr. Gosin
Related Party Transaction
Stock redeemed or called during period (in shares)			478,328
Stock redeemed or called during period, value | $			$ 0
Number of non exchangeable PSU converted (in shares)					443,871.6
Non Exchangeable PSU | Mr. Gosin | BGC Partners Inc
Related Party Transaction
Number of non exchangeable PSU converted (in shares)					1,592,016
Non Exchangeable PSU | Mr. Gosin | Class A Common Stock | BGC Partners Inc
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)				2,114,456
Payment for exchangeable PSUs redeemed | $				$ 0
Non Exchangeable PSU | Howard W. Lutnick
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)					193,530
Stock redeemed or called during period (in shares)			286,511
Stock redeemed or called during period, value | $			$ 0
Number of non exchangeable PSU converted (in shares)					552,482.62
Non Exchangeable PSU | Howard W. Lutnick | BGC Partners Inc
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)					88,636
Number of non exchangeable PSU converted (in shares)					1,131,774
Non Exchangeable PSU | Mr. Merkel
Related Party Transaction
Number of share issued for non exchangeable PPSU (in shares)						145,384
Exchangeable PPSU | Michael J. Rispoli
Related Party Transaction
Cash payment to redeem | $					$ 208,407
Exchangeable PPSU | Howard W. Lutnick
Related Party Transaction
Stock redeemed or called during period (in shares)			193,530
Stock redeemed or called during period, value | $			$ 1,465,873
Non Exchangeable NPPSU | Howard W. Lutnick
Related Party Transaction
Cash payment to redeem non exchangeable shares | $			1,284,376
Fees to related parties | $			$ 4,406,915
Number of non exchangeable NPPSU redeemed (in shares)			127,799
Number of non exchangeable NPPSU monetized (in shares)			122,201
Payment to redeem non exchangeable monetized shares, net | $			$ 1,228,124
Non Exchangeable A P S U | Mr. Gosin
Related Party Transaction
Number of non exchangeable PSU redeemed (in shares)							30,871
Non Exchangeable HDU | Michael J. Rispoli
Related Party Transaction
Number of non exchangeable HUD (in shares)					5,846
Non Exchangeable HDU | Mr. Gosin
Related Party Transaction
Number of non exchangeable HUD (in shares)					443,871.6
Payment to convert non exchangeable shares, net | $					$ 5,362,452
Non Exchangeable HDU | Mr. Gosin | BGC Partners Inc
Related Party Transaction
Share price (in dollars per share) | $ / shares		$ 3.89
Number of non exchangeable HUD (in shares)					1,592,016
Non Exchangeable HDU | Mr. Gosin | Class A Common Stock | BGC Partners Inc
Related Party Transaction
Number of exchangeable HDUs redeemed (in shares)		905,371
Payment for exchangeable HDUs redeemed | $		$ 3,521,893
Non Exchangeable HDU | Howard W. Lutnick
Related Party Transaction
Cash payment to redeem non exchangeable shares | $					$ 7,983,000
Number of non exchangeable HUD (in shares)					552,482.62
Non Exchangeable H U D, Capital Account | $					$ 7,017,000
Non Exchangeable HDU | Howard W. Lutnick | Class A Common Stock | BGC Partners Inc
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)					29,059
Restricted Stock | Michael J. Rispoli
Related Party Transaction
Limited partnership units exchange ratio					0.9403
Restricted Stock | Michael J. Rispoli | Class A Common Stock
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)					5,642
Restricted Stock | Howard W. Lutnick
Related Party Transaction
Limited partnership units exchange ratio					0.9403
Holdings Unit | Mr. Gosin
Related Party Transaction
Number of exchangeable (in shares)					1,531,061.84
Holdings Unit | Mr. Gosin | BGC Partners Inc
Related Party Transaction
Number of exchangeable (in shares)					3,348,706
Exchangeable APSU | Mr. Gosin
Related Party Transaction
Number of exchangeable (in shares)					92,464.47
Exchangeable APSU | Mr. Gosin | BGC Partners Inc
Related Party Transaction
Number of exchangeable (in shares)					201,621
Holdings PSU | Michael J. Rispoli | BGC Partners Inc
Related Party Transaction
Number of exchangeable (in shares)					36,985