Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities:
Consolidated net loss	$ (187,538)	$ (30,690)	$ (128,153)
Adjustments to reconcile consolidated net loss to net cash used for operating activities:
Net fair value adjustments	117,247	144,990	100,688
Change in fair value of loan servicing assets and liabilities	58,730	58,095	30,482
Stock-based compensation, net	61,533	73,639	75,087
Goodwill impairment charge	0	0	35,633
Depreciation and amortization	54,029	59,152	54,764
Gain on sales of loans	(30,812)	(67,716)	(50,421)
Other, net	8,922	7,483	5,471
Purchase of loans held for sale	(2,779,493)	(7,643,996)	(7,397,886)
Principal payments received on loans held for sale	233,310	265,820	210,831
Proceeds from whole loan sales and Structured Program transactions, net of underwriting fees and costs	2,981,428	6,937,984	6,485,432
Net change in operating assets and liabilities:
Accrued interest receivable, net	(5,048)	(16,298)	(3,785)
Other assets	19,728	6,609	52,708
Accounts payable	(6,922)	4,158	(3,005)
Accrued interest payable	(4,688)	(9,843)	(13,372)
Accrued expenses and other liabilities	(41,824)	326	(93,424)
Payable to investors	(60,571)	(60,357)	(791)
Net cash provided by (used for) operating activities	418,031	(270,644)	(639,741)
Cash Flows from Investing Activities:
Purchase of loans	(315,135)	(633,632)	(960,881)
Principal payments received on loans held for sale	691,536	1,191,428	1,763,348
Proceeds from recoveries and sales of charged-off loans	42,178	54,032	63,240
Purchases of securities available for sale	(53,736)	(144,481)	(136,445)
Proceeds from sales, maturities, redemptions and paydowns of securities available for sale	99,630	145,880	153,468
Proceeds from paydowns of asset-backed securities related to Structured Program transactions	132,045	90,648	47,235
Purchases of property, equipment and software, net	(31,147)	(50,668)	(52,976)
Other investing activities	400	561	1,747
Net cash provided by investing activities	565,771	653,768	878,736
Cash Flows from Financing Activities:
Proceeds from issuance of notes and certificates	314,995	632,962	953,904
Repayments of secured borrowings	(16,867)	(56,884)	(139,206)
Principal payments on and retirements of notes and certificates	(671,359)	(1,147,297)	(1,615,800)
Payments on notes and certificates from recoveries/sales of related charged-off loans	(41,179)	(55,022)	(62,494)
Principal payments on securitization notes	(73,710)	(58,025)	(45,709)
Proceeds from issuance of securitization notes and certificates	186,190	42,500	258,767
Proceeds from credit facilities and securities sold under repurchase agreements	1,195,261	2,943,948	2,125,488
Principal payments on credit facilities and securities sold under repurchase agreements	(1,676,618)	(2,815,475)	(1,698,214)
Payment for debt issuance costs	(1,852)	(1,419)	(4,494)
Net cash inflow (outflow) from consolidation (deconsolidation) of VIE	0	(5,951)	(15,013)
Dividends paid on preferred stock	(50,204)	0	0
Other financing activities	(7,096)	(19,397)	3,545
Net cash used for financing activities	(842,439)	(540,060)	(239,226)
Net Increase (Decrease) in Cash, Cash Equivalents and Restricted Cash	141,363	(156,936)	(231)
Cash, Cash Equivalents and Restricted Cash, Beginning of Period	487,122	644,058	644,289
Cash, Cash Equivalents and Restricted Cash, End of Period	628,485	487,122	644,058
Supplemental Cash Flow Information:
Cash paid for interest	143,840	254,585	394,459
Cash paid for operating leases included in the measurement of lease liabilities	16,679	16,816	0
Non-cash investing activity:
Accruals for property, equipment and software	686	1,745	2,256
Securities retained from Structured Program transactions	43,458	197,267	106,609
Non-cash investing and financing activity:
Transfer of whole loans to redeem certificates	17,414	122,330	1,095
Non-cash financing activity:
Exchange of common stock for preferred stock	207,244	0	0
Derecognition of payable to securitization note and residual certificate holders held in consolidated VIE	$ 0	$ 200,881	$ 269,151