Segment Reporting - Reconciliation of Operating Profit (Loss) from Segments to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	$ 142,642	$ 104,935	$ 222,536	$ 164,802
Cost of revenue	97,429	67,975	171,626	121,467
Gross profit	45,213	36,960	50,910	43,335
Operating expenses	42,756	32,688	85,628	67,186
Net income (loss)	3,207	4,304	(33,232)	(23,762)	$ (15,002)
Operating Segments | Real estate services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	130,858	100,658	205,783	159,030
Cost of revenue	85,337	63,436	153,501	114,592
Gross profit	45,521	37,222	52,282	44,438
Operating Segments | Properties
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	8,986	1,981	12,038	1,981
Cost of revenue	9,088	2,030	12,430	2,036
Gross profit	(102)	(49)	(392)	(55)
Other revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenue	2,798	2,296	4,715	3,791
Cost of revenue	3,004	2,509	5,695	4,839
Gross profit	$ (206)	$ (213)	$ (980)	$ (1,048)