Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 140,255	$ 109,479	$ 362,791	$ 274,282
Other revenue
Disaggregation of Revenue [Line Items]
Revenue	2,640	2,251	7,356	6,043
Real estate services
Disaggregation of Revenue [Line Items]
Revenue	126,265	103,864	332,047	262,894
Real estate services | Brokerage revenue
Disaggregation of Revenue [Line Items]
Revenue	118,809	97,787	312,306	247,327
Real estate services | Partner revenue
Disaggregation of Revenue [Line Items]
Revenue	7,456	6,077	19,741	15,567
Properties
Disaggregation of Revenue [Line Items]
Revenue	$ 11,350	$ 3,364	$ 23,388	$ 5,345