Summary of Significant Accounting Policies - Disaggregated revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 90,997	$ 71,073	$ 240,538	$ 193,552
Franchise sales and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	7,052	5,349	21,130	20,124
Total Real Estate
Disaggregation of Revenue [Line Items]
Total revenue	64,623	50,952	172,068	139,228
Total Real Estate | Fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	58,628	46,894	154,223	123,102
Total Real Estate | Franchise sales and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	5,995	4,058	17,845	16,126
Total Marketing Funds
Disaggregation of Revenue [Line Items]
Total revenue	23,269	17,290	59,456	46,577
Mortgage
Disaggregation of Revenue [Line Items]
Total revenue	2,620	1,906	7,353	4,434
Mortgage | Franchise sales and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	572	366	1,624	685
Other
Disaggregation of Revenue [Line Items]
Total revenue	485	925	1,661	3,313
U.S. | Company -Owned Regions | Fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	42,922	35,286	113,081	91,375
U.S. | Independent Regions | Fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	2,592	3,604	9,610	9,767
U.S. | Total Marketing Funds
Disaggregation of Revenue [Line Items]
Total revenue	18,471	15,701	51,012	41,948
Canada | Company -Owned Regions | Fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	8,889	3,579	17,243	9,119
Canada | Independent Regions | Fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	1,258	2,090	5,827	6,162
Canada | Total Marketing Funds
Disaggregation of Revenue [Line Items]
Total revenue	4,541	1,405	7,702	4,075
Global | Global. | Fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	2,967	2,335	8,462	6,679
Global | Total Marketing Funds
Disaggregation of Revenue [Line Items]
Total revenue	$ 257	$ 184	$ 742	$ 554