| Cover Page | Feb. 18, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 18, 2020 |
| Entity Registrant Name | Newmark Group, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-38329 |
| Entity Tax Identification Number | 81-4467492 |
| Entity Address, Address Line One | 125 Park Avenue |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10017 |
| City Area Code | 212 |
| Local Phone Number | 372-2000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A Common Stock, $0.01 par value |
| Trading Symbol | NMRK |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001690680 |
| Amendment Flag | false |
