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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	$ 197,780	$ 142,642	$ 307,922	$ 222,536
Cost of revenue	149,434	97,429	256,821	171,626
Gross profit	48,346	45,213	51,101	50,910
Operating expenses	60,767	42,756	130,972	85,628
Interest income	1,913	729	4,229	1,307
Interest expense	(2,153)	0	(4,290)	0
Other income, net	36	21	128	179
Net income (loss)	(12,625)	3,207	(79,804)	(33,232)
Operating Segments \| Real estate services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	152,846	130,858	238,736	205,783
Cost of revenue	103,616	85,337	184,399	153,501
Gross profit	49,230	45,521	54,337	52,282
Operating Segments \| Properties
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	39,908	8,986	61,281	12,038
Cost of revenue	40,906	9,088	63,898	12,430
Gross profit	(998)	(102)	(2,617)	(392)
Other revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	5,281	2,798	8,329	4,715
Cost of revenue	5,167	3,004	8,948	5,695
Gross profit	114	(206)	(619)	(980)
Intercompany eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	(255)	0	(424)	0
Cost of revenue	(255)	0	(424)	0
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]
Revenue	145,399	123,355	226,713	193,498
Partner revenue \| Operating Segments \| Real estate services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	$ 7,447	$ 7,503	$ 12,023	$ 12,285

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