Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,353,138	$ 773,987	$ 784,108
New York City
Disaggregation of Revenue [Line Items]
Total revenues	482,134	247,075	376,600
Northeast
Disaggregation of Revenue [Line Items]
Total revenues	251,539	207,437	171,677
Southeast
Disaggregation of Revenue [Line Items]
Total revenues	387,498	182,485	126,181
West
Disaggregation of Revenue [Line Items]
Total revenues	231,967	136,990	109,650
Commission and other brokerage income - existing home sales
Disaggregation of Revenue [Line Items]
Total revenues	1,210,469	686,389	669,489
Commission and other brokerage income - existing home sales | New York City
Disaggregation of Revenue [Line Items]
Total revenues	392,011	186,229	293,009
Commission and other brokerage income - existing home sales | Northeast
Disaggregation of Revenue [Line Items]
Total revenues	249,195	204,814	164,724
Commission and other brokerage income - existing home sales | Southeast
Disaggregation of Revenue [Line Items]
Total revenues	355,206	160,404	106,587
Commission and other brokerage income - existing home sales | West
Disaggregation of Revenue [Line Items]
Total revenues	214,057	134,942	105,169
Commission and other brokerage income - existing home sales
Disaggregation of Revenue [Line Items]
Total revenues	81,947	47,362	72,925
Commission and other brokerage income - existing home sales | New York City
Disaggregation of Revenue [Line Items]
Total revenues	48,167	24,590	48,850
Commission and other brokerage income - existing home sales | Northeast
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Commission and other brokerage income - existing home sales | Southeast
Disaggregation of Revenue [Line Items]
Total revenues	32,292	22,081	19,594
Commission and other brokerage income - existing home sales | West
Disaggregation of Revenue [Line Items]
Total revenues	1,488	691	4,481
Property management revenue
Disaggregation of Revenue [Line Items]
Total revenues	37,345	35,115	35,461
Property management revenue | New York City
Disaggregation of Revenue [Line Items]
Total revenues	36,756	34,209	34,741
Property management revenue | Northeast
Disaggregation of Revenue [Line Items]
Total revenues	589	906	720
Property management revenue | Southeast
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Property management revenue | West
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Title fees
Disaggregation of Revenue [Line Items]
Total revenues	23,377	5,121	6,233
Title fees | New York City
Disaggregation of Revenue [Line Items]
Total revenues	5,200	2,047	0
Title fees | Northeast
Disaggregation of Revenue [Line Items]
Total revenues	1,755	1,717	6,233
Title fees | Southeast
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Title fees | West
Disaggregation of Revenue [Line Items]
Total revenues	$ 16,422	$ 1,357	$ 0