Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities
Net income (loss)	$ (240,132)	$ (108,665)	$ 135,443
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Change in fair value of financial instruments	234,822	168,878	(228)
Stock-based compensation	175,039	125,945	73,186
Gain on loan servicing rights, net	(13,713)	(28,739)	(6,916)
Depreciation and amortization	24,903	13,513	7,541
Non-cash interest expense	3,057	3,047	1,983
Other	(3,869)	0	0
Net changes in operating assets and liabilities:
Purchases of loans held-for-sale	(3,006,510)	(7,807,429)	(8,932,604)
Proceeds from sale of loans held-for-sale	2,514,627	6,828,617	8,826,045
Principal payments received for loans held-for-sale	189,746	152,018	8,659
Principal payments received for loans held by consolidated securitization	24,832	0	0
Settlements of beneficial interest liabilities	(596)	0	0
Other assets	(8,932)	4,173	(62,042)
Operating lease liability and right-of-use asset	(6,822)	10,204	3,126
Accounts payable	(6,127)	11,878	(7,513)
Payable to investors	(42,989)	(16,821)	62,097
Accrued expenses and other liabilities	2,171	(31,300)	59,576
Net cash provided by (used in) operating activities	(160,493)	(674,681)	168,353
Cash flows from investing activities
Purchases and originations of loans held-for-investment	(157,223)	(149,298)	(159,398)
Proceeds from sale of loans held-for-investment	972	14,289	51,403
Principal payments received for loans held-for-investment	102,446	43,311	24,532
Principal payments received for notes receivable and repayments of residual certificates	4,328	6,736	11,458
Purchases of property and equipment	(1,527)	(8,825)	(8,427)
Capitalized software costs	(10,559)	(14,088)	(6,688)
Acquisition of beneficial interest assets	(56,892)	0	0
Purchases of non-marketable equity securities	0	(1,250)	(40,000)
Purchase of certificates of deposit	0	(5,000)	0
Acquisition, net of cash acquired	0	0	(16,757)
Net cash used in investing activities	(118,455)	(114,125)	(143,877)
Cash flows from financing activities
Proceeds from borrowings	626,910	688,813	718,422
Repayments of borrowings	(575,937)	(400,898)	(71,316)
Principal payments made on securitization notes	(23,320)	0	0
Proceeds from issuance of securitization notes	165,318	0	0
Proceeds from secondary offering, net of underwriting discounts, commissions, and offering costs	0	0	263,931
Payment of debt issuance costs	0	0	(15,727)
Purchase of capped calls	0	0	(58,523)
Proceeds from issuance of common stock under employee stock purchase plan	8,431	7,662	4,145
Proceeds from exercise of stock options	12,881	12,354	14,736
Taxes paid related to net share settlement of equity awards	(15)	(16)	(236)
Repurchases of common stock	0	(177,883)	0
Net cash provided by financing activities	214,268	130,032	855,432
Change in cash and restricted cash	(64,680)	(658,774)	879,908
Cash and restricted cash at beginning of year	532,467	1,191,241	311,333
Cash and restricted cash at end of year	467,787	532,467	1,191,241
Supplemental disclosures of cash flow information
Cash paid for interest	36,547	12,473	3,274
Cash (received) paid for income taxes, net	(658)	328	2,300
Supplemental disclosures of non-cash investing and financing activities
Securities retained under consolidated securitization transaction	44,763	0	0
Residual certificates retained under unconsolidated securitization	13,172	4,680	0
Beneficial interest assets included in payable to investors	5,792	0	0
Capitalized stock-based compensation expense	6,666	5,960	3,141
Issuance of common stock in connection with acquisition	0	0	80,256
Cash and Restricted Cash
Cash	368,405	422,411
Restricted cash	99,382	110,056
Total cash and restricted cash	$ 467,787	$ 532,467	$ 1,191,241