Segment Reporting and Revenue - Reconciliation of Operating Profit (Loss) from Segments to Consolidated (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	$ 779,796	$ 486,920	$ 370,036
Cost of revenue	635,693	367,496	258,216
Gross profit	144,103	119,424	111,820
Operating expenses	223,349	163,358	127,792
Interest income	7,146	5,416	882
Interest expense	(8,928)	(3,681)	0
Other income, net	223	221	88
Net loss	(80,805)	(41,978)	(15,002)
Operating Segments | Real estate services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	523,540	432,168	351,570
Cost of revenue	373,150	309,069	237,832
Gross profit	150,390	123,099	113,738
Operating Segments | Real estate services | Brokerage revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	496,480	406,293	330,372
Operating Segments | Real estate services | Partner revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	27,060	25,875	21,198
Operating Segments | Properties
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	240,507	44,993	10,491
Cost of revenue	245,189	46,613	10,384
Gross profit	(4,682)	(1,620)	107
Operating Segments | Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	17,634	9,882	7,975
Cost of revenue	19,239	11,937	10,000
Gross profit	(1,605)	(2,055)	(2,025)
Intercompany eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	(1,885)	(123)	0
Cost of revenue	(1,885)	(123)	0
Gross profit	$ 0	$ 0	$ 0