Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Operating activities
Net loss	$ (36,439)	$ (28,066)	$ (15,002)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,003	1,905
Stock-based compensation	4,196	2,681
Change in assets and liabilities:
Prepaid expenses	3,852	1,086
Accrued revenue	1,241	(1,650)
Other current assets	(3,661)	(1,582)
Other long-term assets	(103)	384
Accounts payable	1,029	(2,912)
Accrued liabilities	7,248	5,839
Deferred lease liability	(268)	501
Origination of loans held for sale	(9,477)	0
Proceeds from sale of loans originated as held for sale	9,887	0
Net cash used in operating activities	(20,492)	(21,814)
Investing activities
Maturities and sales of short-term investments	0	1,251
Purchases of short-term investments	0	(1,252)
Purchases of property and equipment	(2,305)	(4,781)
Net cash used in investing activities	(2,305)	(4,782)
Financing activities
Proceeds from exercise of stock options	5,946	551
Tax payment related to net share settlements on restricted stock units	(59)	0
Payment of initial public offering costs	0	(1,579)
Borrowings from warehouse credit facilities	9,265	0
Repayments of warehouse credit facilities	(9,924)	0
Other payables - customer escrow deposits related to title services	6,808	4,651
Net cash provided by financing activities	12,036	3,623
Net change in cash and cash equivalents, and restricted cash	(10,761)	(22,973)
Cash, cash equivalents, and restricted cash:
Beginning of period	212,658	67,845	67,845
End of period	201,897	44,872	$ 212,658
Supplemental Cash Flow Information [Abstract]
Accretion of redeemable convertible preferred stock	0	(24,770)
Stock-based compensation capitalized in property and equipment	(124)	(74)
Initial public offering cost accruals	0	(190)
Property and equipment additions in accounts payable and accrued expenses	(55)	(37)
Leasehold improvements paid directly by lessor	0	(104)
Cash-in-transit for exercised stock options	$ (56)	$ 0