Segment Reporting and Revenue - Reconciliation of Operating Profit (Loss) from Segments to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	$ 213,665	$ 197,780	$ 404,660	$ 307,922
Cost of revenue	167,626	149,434	345,742	256,821
Gross profit	46,039	48,346	58,918	51,101
Operating expenses	50,465	60,767	120,774	130,972
Interest income	437	1,913	1,540	4,229
Interest expense	(2,665)	(2,153)	(5,109)	(4,290)
Other income (expense), net	43	36	(1,303)	128
Net loss	(6,611)	(12,625)	(66,728)	(79,804)
Operating Segments \| Real estate services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	135,049	152,846	243,685	238,736
Cost of revenue	88,799	103,616	182,361	184,399
Gross profit	46,250	49,230	61,324	54,337
Operating Segments \| Properties
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	72,184	39,908	151,282	61,281
Cost of revenue	73,348	40,906	152,647	63,898
Gross profit	(1,164)	(998)	(1,365)	(2,617)
Other revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	7,246	5,281	11,496	8,329
Cost of revenue	6,293	5,167	12,537	8,948
Gross profit	953	114	(1,041)	(619)
Intercompany eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Cost of revenue	(814)	(255)	(1,803)	(424)
Gross profit	0	0	0	0
Brokerage revenue \| Operating Segments \| Real estate services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	128,543	145,399	230,894	226,713
Partner revenue \| Operating Segments \| Real estate services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	$ 6,506	$ 7,447	$ 12,791	$ 12,023

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