Segment Reporting and Revenue - Reconciliation of Operating Profit (Loss) from Segments to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	$ 236,916	$ 238,683	$ 641,576	$ 546,605
Cost of revenue	143,844	185,306	489,586	442,127
Gross profit	93,072	53,377	151,990	104,478
Operating expenses	56,063	45,941	176,837	176,913
Interest income	319	1,576	1,859	5,804
Interest expense	(2,522)	(2,274)	(7,631)	(6,564)
Other income (expense), net	(640)	44	(1,943)	172
Net loss	34,166	6,782	(32,562)	(73,023)
Operating Segments \| Real estate services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	209,853	154,126	453,538	392,862
Cost of revenue	117,944	100,048	300,305	284,447
Gross profit	91,909	54,078	153,233	108,415
Operating Segments \| Properties
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	19,005	80,164	170,287	141,445
Cost of revenue	20,460	80,909	173,107	144,807
Gross profit	(1,455)	(745)	(2,820)	(3,362)
Other revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	8,503	5,161	19,999	13,490
Cost of revenue	5,885	5,117	18,422	14,065
Gross profit	2,618	44	1,577	(575)
Intercompany eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Cost of revenue	(445)	(768)	(2,248)	(1,192)
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	194,375	146,096	425,269	372,809
Partner revenue \| Operating Segments \| Real estate services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Brokerage revenue	$ 15,478	$ 8,030	$ 28,269	$ 20,053

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