Acquisitions - Additional Information (Detail) $ in Thousands	1 Months Ended		12 Months Ended
	Jul. 31, 2018 Office	Apr. 30, 2018 Office	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Contingent consideration			$ 32,065	$ 28,099
Additional goodwill recognized			557,914	515,321	$ 477,532
Business acquisition, aggregate revenue contribution			18,400	28,500
Number of offices acquired | Office	2	2
2019 Acquisitions
Business Acquisition [Line Items]
Total consideration transferred			60,600
Contingent consideration			15,300
Additional goodwill recognized			43,804
Business acquisition, amount deductible for tax			$ 29,700
2019 Acquisitions | Newmark Holdings, L.P. | Limited Partnership Units
Business Acquisition [Line Items]
Business acquisition price paid (Partnership Units) (in shares) | shares			327,692,000,000
Business acquisition, contingent non cash consideration, fair value			$ 2,700
2018 Acquisitions
Business Acquisition [Line Items]
Total consideration transferred				62,900
Contingent consideration				8,600
Additional goodwill recognized				42,188
Business acquisition, amount deductible for tax				$ 28,600
2018 Acquisitions | Restricted Stock
Business Acquisition [Line Items]
Business acquisition price paid (Partnership Units) (in shares) | shares				216,900
Business acquisition, contingent non cash consideration, fair value				$ 3,100
2018 Acquisitions | Newmark Holdings, L.P. | Limited Partnership Units
Business Acquisition [Line Items]
Business acquisition price paid (Partnership Units) (in shares) | shares				465,316
Business acquisition, contingent non cash consideration, fair value				$ 6,200