Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating Activities
Net loss	$ (63,662,000)	$ (66,728,000)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	18,018,000	6,865,000
Stock-based compensation	26,327,000	14,416,000
Amortization of debt discount and issuance costs	2,203,000	3,477,000
Non-cash lease expense	5,448,000	4,522,000
Impairment costs	0	1,420,000
Net loss (gain) on IRLCs, forward sales commitments, and loans held for sale	238,000	(1,928,000)
Other	169,000	(218,000)
Change in assets and liabilities:
Accounts receivable, net	(22,312,000)	(14,959,000)
Inventory	(199,845,000)	65,153,000
Prepaid expenses and other assets	(7,137,000)	6,827,000
Accounts payable	15,766,000	1,040,000
Accrued liabilities, other payables, deferred tax liabilities, and payroll tax liabilities, noncurrent	26,915,000	13,819,000
Lease liabilities	(6,144,000)	(5,481,000)
Origination of loans held for sale	(488,274,000)	(294,076,000)
Proceeds from sale of loans originated as held for sale	478,652,000	274,595,000
Net cash (used in) provided by operating activities	(213,638,000)	8,744,000
Investing activities
Purchases of property and equipment	(13,580,000)	(6,072,000)
Purchases of investments	(104,877,000)	(88,724,000)
Sales of investments	89,536,000	3,183,000
Maturities of investments	92,843,000	40,351,000
Cash paid for acquisition	(608,000,000)	0
Net cash used in investing activities	(544,078,000)	(51,262,000)
Financing activities
Proceeds from the issuance of convertible preferred stock, net of issuance costs	0	39,801,000
Proceeds from the issuance of common stock, net of issuance costs	0	69,701,000
Proceeds from the issuance of common stock pursuant to employee equity plans	12,496,000	11,052,000
Tax payments related to net share settlements on restricted stock units	(16,530,000)	(6,065,000)
Borrowings from warehouse credit facilities	464,250,000	290,891,000
Repayments to warehouse credit facilities	(456,854,000)	(271,627,000)
Borrowings from secured revolving credit facility	230,608,000	39,587,000
Repayments to secured revolving credit facility	(130,788,000)	(36,816,000)
Proceeds from issuance of convertible senior notes, net of issuance costs	561,529,000	0
Purchases of capped calls related to convertible senior notes	(62,647,000)	0
Payments for repurchases and conversions of convertible senior notes	(1,925,000)	0
Other payables—deposits held in escrow	97,000	19,056,000
Principal payments under finance lease obligations	(353,000)	(30,000)
Cash paid for secured revolving credit facility issuance costs	(305,000)	(4,000)
Net cash provided by financing activities	599,578,000	155,546,000
Effect of exchange rate changes on cash, cash equivalents, and restricted cash	0	(22,000)
Net change in cash, cash equivalents, and restricted cash	(158,138,000)	113,006,000
Cash, cash equivalents, and restricted cash:
Beginning of period	945,820,000	247,448,000
End of period	787,682,000	360,454,000
Supplemental disclosure of cash flow information
Cash paid for interest	2,038,000	2,133,000
Non-cash transactions
Stock-based compensation capitalized in property and equipment	1,717,000	1,151,000
Property and equipment additions in accounts payable and accrued liabilities	1,013,000	1,492,000
Leasehold improvements paid directly by lessor	$ 1,334,000	$ 0