Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net income (loss)	$ (13,203)	$ (17,191)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	5,326	4,532
Stock-based compensation	8,028	5,890
Change in assets and liabilities:
Restricted cash	(6,286)	(3,371)
Prepaid expenses	(84)	2,755
Accrued revenue	(2,712)	(5,423)
Other current assets	3,157	(1,838)
Other long-term assets	244	(5,953)
Accounts payable	1,227	1,858
Accrued expenses	8,513	7,086
Other payables	6,065	3,362
Deferred lease liability	1,001	1,770
Origination of loans held for sale	(5,755)	0
Proceeds from sale of loans originated as held for sale	5,030	0
Net cash provided by (used in) operating activities	10,551	(6,523)
Investing activities
Maturities and sales of short-term investments	1,484	1,744
Purchases of short-term investments	(993)	(1,744)
Purchases of property and equipment	(10,499)	(5,116)
Net cash used in investing activities	(10,008)	(5,116)
Financing activities
Proceeds from exercise of stock options	2,519	1,069
Payment of initial public offering costs	(3,449)	0
Proceeds from initial public offering, net of underwriting discounts	148,088	0
Borrowings from warehouse credit facilities	5,603	0
Repayments of warehouse credit facilities	(4,898)	0
Net cash provided by financing activities	147,863	1,069
Net change in cash and cash equivalents	148,406	(10,570)
Cash and cash equivalents:
Beginning of period	64,030	85,597
End of period	212,436	75,027
Supplemental disclosure of non-cash investing and financing activities
Accretion of redeemable convertible preferred stock	(175,915)	56,819
Stock-based compensation capitalized in property and equipment	(194)	(57)
Initial public offering cost accruals	(200)	0
Leasehold improvements paid directly by lessor	$ (104)	$ 0