Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 142,642	$ 104,935	$ 222,536	$ 164,802
Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,798	2,296	4,715	3,791
Real estate services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	130,858	100,658	205,783	159,030
Real estate services | Brokerage revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	123,355	95,069	193,498	149,540
Real estate services | Partner revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	7,503	5,589	12,285	9,490
Properties
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 8,986	$ 1,981	$ 12,038	$ 1,981