Organization and Basis of Presentation (Details) $ / shares in Units, $ in Thousands								12 Months Ended				46 Months Ended
	Jul. 02, 2021 USD ($) shares	Jun. 28, 2021 USD ($) $ / shares shares	Jun. 25, 2021 shares	Nov. 30, 2020 USD ($) shares	Dec. 02, 2019 USD ($) shares	Sep. 26, 2018 USD ($) tranche shares	Jun. 28, 2013 USD ($) shares	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) shares	Dec. 31, 2018 USD ($)	Jun. 30, 2021 USD ($) shares	Jul. 31, 2021 $ / shares	Jun. 18, 2018 USD ($)
Description Of Business
Shares settled (in shares) | shares				741,505	898,685
Investment owned shares settled fair value				$ 93,500	$ 93,500
Shares owned (in shares) | shares				250,742	93,562
Marketable securities								$ 99	$ 788
Compensation expense								124,805	122,437	$ 301,162
Deferred tax asset, net of allowance								$ 180,976	171,524
Amount received from the value of shares pledged									$ 140,000	$ 106,700
2021 Equity Event
Description Of Business
Compensation expense		$ 428,600
Deferred tax asset, net of allowance		$ 101,000
Settlement share price (in usd per share) | $ / shares		$ 12.50											$ 13.01
2021 Equity Event | Class A Common Stock
Description Of Business
Limited partnership units conversion ratio												0.9403
Common Stock | Nasdaq
Description Of Business
Marketable securities												$ 1,093,900
Common Stock | Nasdaq | Nasdaq
Description Of Business
Number of shares pledged to be repurchased (in shares) | shares										866,791
Value of shares pledged to be repurchased										$ 182,000
Amount received from the value of shares pledged										$ 140,000
Common Stock | Nasdaq Earn-Out
Description Of Business
Marketable securities	$ 166,000			$ 121,900	$ 98,600
Shares settled (in shares) | shares	944,329		6,222,340
Newmark Holdings, L.P. | Employees | Limited Partnership Units
Description Of Business
Shares redeemed or exchanged (in shares) | shares		8,300,000
Newmark Holdings, L.P. | Independent Contractors | Limited Partnership Units
Description Of Business
Shares redeemed or exchanged (in shares) | shares		23,200,000
BGC Holdings, L.P. | Employees | Limited Partnership Units
Description Of Business
Shares redeemed or exchanged (in shares) | shares		8,000,000
BGC Holdings, L.P. | Independent Contractors | Limited Partnership Units
Description Of Business
Shares redeemed or exchanged (in shares) | shares		17,400,000
Nasdaq Omx | Maximum
Description Of Business
Shares received from transaction (in shares) | shares						992,247
Nasdaq Omx | eSpeed
Description Of Business
Purchase consideration paid in cash							$ 750,000
Period for expected payment under Common stock transaction							15 years
Amount recognized in connection with the earn-out including other income (loss) (in shares) | shares												10,200,000
Shares sold under common stock transactions (in shares) | shares												7,600,000
Common stock transactions, realized gain and dividend income												$ 1,474,200
Nasdaq Omx | eSpeed | Maximum | BGC Partners Inc
Description Of Business
Expected payment of shares under common stock transaction (in shares) | shares							14,883,705
Nasdaq Omx | eSpeed | Minimum | BGC Partners Inc
Description Of Business
Gross revenue on expected payment per year under common stock transaction							$ 25,000
RBC | Newmark OpCo
Description Of Business
Exchangeable preferred limited partnership units issued (in shares)						$ 150,000								$ 175,000
Proceeds from issuance of EPUs											$ 266,100
Exchangeable preferred limited partnership units, number of tranches | tranche						4
RBC | eSpeed
Description Of Business
Shares delivered under common stock transactions (in shares) | shares												2,600,000