Compensation - Units Redeemed in Connection with Issuance of Class A Common Stock (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units redeemed (in shares)	291,721	88,545
BGC Holdings, L.P.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units redeemed (in shares)	149,280	58,855
NEWMARK Group Inc Parent
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units redeemed (in shares)	142,441	29,690