Stock Transactions and Unit Redemptions - Schedule of Changes in Shares of Common Stock Outstanding (Detail) - Class A Common Stock - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at beginning of period (in shares)	156,265,461	156,916,336
Share issuances:
LPU redemption/exchange (in shares)	181,872	374,930
Other issuances of Class A common stock (in shares)		8,451
Shares outstanding at end of period (in shares)	156,701,746	157,422,916
Restricted Stock Units (RSUs)
Share issuances:
Issuance of Class A common stock for Newmark RSUs (in shares)	254,413	123,199