Operating Segments - Schedule of Real Estate Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total real estate revenue	$ 370,036	$ 267,196	$ 187,338
Real Estate
Segment Reporting Information [Line Items]
Total real estate revenue	351,570	260,383	181,446
Brokerage Revenue | Real Estate
Segment Reporting Information [Line Items]
Total real estate revenue	330,372	244,079	171,276
Partner Revenue | Real Estate
Segment Reporting Information [Line Items]
Total real estate revenue	$ 21,198	$ 16,304	$ 10,170