Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Activities
Net loss	$ (109,613)	$ (18,527)	$ (80,805)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	46,906	14,564	9,230
Stock-based compensation	54,722	36,973	27,814
Amortization of debt discount and issuance costs	4,989	12,038	6,385
Non-cash lease expense	11,630	9,204	6,940
Impairment costs	0	2,063	0
Loss on repurchases and conversions of convertible senior notes	0	4,634	0
Net loss (gain) on IRLCs, forward sales commitments, and loans held for sale	815	(1,921)	(493)
Other	(4,227)	(349)	(662)
Change in assets and liabilities:
Accounts receivable, net	(7,149)	(35,496)	(3,861)
Inventory	(309,063)	25,432	(51,896)
Prepaid expenses and other assets	(12,248)	2,333	(3,293)
Accounts payable	3,059	2,086	(394)
Accrued and other liabilities, deferred tax liabilities, and payroll tax liabilities, noncurrent	25,791	39,092	7,422
Lease liabilities	(13,268)	(11,312)	(7,209)
Origination of loans held for sale	(986,982)	(677,310)	(395,354)
Proceeds from sale of loans originated as held for sale	993,070	657,763	378,566
Net cash (used in) provided by operating activities	(301,568)	61,267	(107,610)
Investing activities
Purchases of property and equipment	(27,492)	(14,686)	(15,533)
Purchases of investments	(146,274)	(198,172)	(136,265)
Sales of investments	98,687	7,887	11,486
Maturities of investments	106,773	147,852	24,400
Cash paid for acquisition	(608,000)	0	0
Net cash used in investing activities	(576,306)	(57,119)	(115,912)
Financing activities
Proceeds from the issuance of convertible preferred stock, net of issuance costs	0	39,801	0
Proceeds from the issuance of common stock, net of issuance costs	0	69,701	0
Proceeds from the issuance of common stock pursuant to employee equity plans	22,772	21,072	16,107
Tax payments related to net share settlements on restricted stock units	(27,066)	(16,852)	(5,126)
Borrowings from warehouse credit facilities	942,993	662,278	388,586
Repayments to warehouse credit facilities	(948,979)	(644,551)	(372,017)
Borrowings from secured revolving credit facility	624,828	89,619	4,444
Repayments to secured revolving credit facility	(448,996)	(70,115)	0
Cash paid for secured revolving credit facility issuance costs	(527)	(4)	(922)
Proceeds from issuance of convertible senior notes, net of issuance costs	561,529	647,486	0
Purchases of capped calls related to convertible senior notes	(62,647)	0	0
Payments for repurchases and conversions of convertible senior notes	(2,159)	(108,061)	0
Principal payments under finance lease obligations	(796)	(221)	(72)
Other financing payables	(10,611)	4,074	883
Net cash provided by financing activities	650,341	694,227	31,883
Effect of exchange rate changes on cash, cash equivalents, and restricted cash	(6)	(3)	32
Net change in cash, cash equivalents, and restricted cash	(227,539)	698,372	(191,607)
Cash, cash equivalents, and restricted cash:
Beginning of period	945,820	247,448	439,055
End of period	718,281	945,820	247,448
Supplemental disclosure of cash flow information
Cash paid for interest	7,592	4,958	2,460
Non-cash transactions
Stock-based compensation capitalized in property and equipment	4,059	2,348	1,280
Property and equipment additions in accounts payable and accrued and other liabilities	659	1,682	223
Leasehold improvements paid directly by lessor	1,334	37	6,230
Issuance of common stock for repurchases and conversions of convertible senior notes	0	98,397	0
Reconciliation of cash, cash equivalents, and restricted cash
Cash and cash equivalents	591,003	925,276	234,679
Restricted cash	127,278	20,544	12,769
Total cash, cash equivalents, and restricted cash	$ 718,281	$ 945,820	$ 247,448