CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Operating activities
Net income	$ 608,325	$ 581,391	$ 469,014
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Provisions for credit losses	408,515	345,463	633,453
Deferred tax provision (benefit)	(34,327)	(23,224)	(93,670)
Amortization of brokered deposit placement fee	10,529	11,681	12,904
Amortization of Secured Borrowing Facility upfront fee	2,359	2,869	2,634
Amortization of deferred loan origination costs and loan premium/(discounts), net	12,883	12,583	14,804
Net amortization of discount on investments	(1,772)	(2,726)	103
Reduction of tax indemnification receivable	0	2,816	5,231
Depreciation of premises and equipment	17,652	17,811	17,331
Acquired intangible assets impairment and amortization expense	5,329	66,364	7,779
Stock-based compensation expense	39,996	36,380	34,461
Unrealized (gains) losses on derivative and hedging activities, net	65	(341)	269
Gains on sale of loans, net	(254,928)	(160,290)	(327,750)
(Gains) losses on securities, net	(467)	(2,678)	60,267
Acquisition transaction costs, net	0	952	2,603
Other adjustments to net income, net	12,563	16,212	14,213
Changes in operating assets and liabilities:
Increase in accrued interest receivable	(1,110,434)	(1,054,071)	(819,958)
Increase in trading investments	0	0	(5,117)
Increase in non-marketable securities	(11,336)	(1,256)	(2,050)
(Increase) decrease in other interest-earning assets	4,349	1,933	(1,507)
Increase in other assets	(6,531)	(38,902)	(23,472)
Increase (decrease) in income tax payable, net	(20,408)	36,723	(15,063)
Increase (decrease) in accrued interest payable	3,423	33,480	24,986
Increase (decrease) in other liabilities	(15,180)	(27,807)	(6,473)
Total adjustments	(937,720)	(726,028)	(464,022)
Total net cash (used in) provided by operating activities	(329,395)	(144,637)	4,992
Investing activities
Loans acquired and originated	(7,064,230)	(6,452,199)	(6,081,389)
Net proceeds from sales of loans held for investment and loans held for sale	4,246,602	3,198,502	3,459,527
Proceeds from FFELP Loan claim payments	27,579	50,145	33,197
Net decrease in loans held for investment and loans held for sale (other than loans acquired and originated, and loan sales)	2,725,473	3,046,064	3,586,825
Purchases of available-for-sale securities	(91,881)	(105,970)	(753,129)
Proceeds from sales and maturities of available-for-sale securities	832,450	265,652	960,015
Purchase of subsidiary, net of cash acquired	0	(14,654)	(127,654)
Total net cash provided by (used in) investing activities	675,993	(12,460)	1,077,392
Financing activities
Brokered deposit placement fee	(7,975)	(7,841)	(11,170)
Net increase in certificates of deposit	88,444	953,412	130,109
Net increase (decrease) in other deposits	(687,108)	(770,485)	570,147
Borrowings collateralized by loans in securitization trusts - issued	2,206,704	1,135,036	572,640
Borrowings collateralized by loans in securitization trusts - repaid	(1,004,117)	(1,154,269)	(1,278,183)
Fees paid on Secured Borrowing Facility	(2,357)	(2,868)	(2,833)
Preferred stock dividends paid	(18,296)	(17,705)	(9,029)
Common stock dividends paid	(99,172)	(101,233)	(112,961)
Common stock repurchased	(247,968)	(350,264)	(713,197)
Net cash provided by (used in) financing activities	228,155	(316,232)	(854,892)
Net increase (decrease) in cash, cash equivalents and restricted cash	574,753	(473,329)	227,492
Cash, cash equivalents and restricted cash at beginning of year	4,299,507	4,772,836	4,545,344
Cash, cash equivalents and restricted cash at end of year	4,874,260	4,299,507	4,772,836
Cash disbursements made for:
Interest	1,109,084	963,260	482,974
Income taxes paid	243,341	191,690	272,940
Income taxes refunded	(1,395)	(8,201)	(2,043)
Reconciliation of the Consolidated Statements of Cash Flows to the Consolidated Balance Sheets:
Cash and cash equivalents	4,700,366	4,149,838	4,616,117
Restricted cash	173,894	149,669	156,719
Total cash, cash equivalents and restricted cash	4,874,260	4,299,507	4,772,836
Supplemental non-cash operating and investing activities:
Accrued interest capitalized during the period	632,504	632,649	589,725
Trading investments received in consideration for loans sold	5,218	5,327	16,477
Available-for-sale investments received in consideration for loans sold	210,371	162,256	222,663
Collateralized Securities
Financing activities
Issuance costs for unsecured debt offering	0	(15)	(40)
Unsecured Debt
Financing activities
Issuance costs for unsecured debt offering	$ 0	$ 0	$ (375)