CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 447,990	$ 436,924
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Provisions for credit losses	409,505	256,691
Income tax expense	146,006	130,798
Amortization of brokered deposit placement fee	14,881	12,292
Amortization of Secured Borrowing Facility upfront fee	2,159	838
Amortization of deferred loan origination costs and loan premium/(discounts), net	20,127	9,750
Net amortization of discount on investments	4,255	1,312
Unrealized gain on investments	(2,100)	0
(Increase) reduction in tax indemnification receivable	(698)	981
Depreciation of premises and equipment	11,386	10,850
Stock-based compensation expense	30,253	24,841
Unrealized gains on derivatives and hedging activities, net	(21,862)	(24,957)
Gains on sales of loans, net	(238,562)	0
Gain on sale of Upromise subsidiary, net	(11,331)	0
Other adjustments to net income, net	5,389	(2,447)
Changes in operating assets and liabilities:
Increase in accrued interest receivable	(668,103)	(719,555)
Increase in non-marketable securities	0	(10,700)
Increase in other interest-earning assets	(1,244)	(47,513)
Decrease in tax indemnification receivable	0	0
Increase in other assets	(46,194)	(10,274)
Decrease in income taxes payable, net	(243,851)	(184,991)
Increase in accrued interest payable	38	21,831
Decrease in Upromise member accounts due to sale	(193,840)	0
Increase in other liabilities	126,645	15,928
Total adjustments	(657,141)	(514,325)
Total net cash used in operating activities	(209,151)	(77,401)
Investing activities
Loans acquired and originated	(4,736,304)	(5,335,986)
Net proceeds from sales of loans held for investment	3,875,984	0
Proceeds from claim payments	22,563	31,474
Net decrease in loans held for investment	2,954,660	2,992,844
Purchases of available-for-sale securities	(1,897,511)	(305,872)
Proceeds from sales and maturities of available-for-sale securities	376,580	32,282
Proceeds from sale of Upromise subsidiary, net	16,922	0
Total net cash provided by (used in) investing activities	612,894	(2,585,258)
Financing activities
Brokered deposit placement fee	(4,810)	(19,799)
Net (decrease) increase in certificates of deposit	(1,802,541)	2,682,850
Net increase in other deposits	501,843	911,985
Borrowings collateralized by loans in securitization trusts - issued	1,337,543	1,105,594
Borrowings collateralized by loans in securitization trusts - repaid	(749,300)	(793,062)
Borrowings under Secured Borrowing Facility	0	297,800
Repayment of borrowings under Secured Borrowing Facility	(289,230)	0
Fees paid on Secured Borrowing Facility	(3,251)	(1,116)
Common stock dividends paid	(35,097)	(38,485)
Preferred stock dividends paid	(8,000)	(12,952)
Common stock repurchased	(558,167)	(157,597)
Net cash (used in) provided by financing activities	(1,611,010)	3,975,218
Net (decrease) increase in cash, cash equivalents and restricted cash	(1,207,267)	1,312,559
Cash, cash equivalents and restricted cash at beginning of period	5,720,760	2,681,895
Cash, cash equivalents and restricted cash at end of period	4,513,493	3,994,454
Cash disbursements made for:
Interest	402,151	489,599
Income taxes paid	248,121	185,138
Income taxes refunded	(4,024)	(853)
Reconciliation of the Consolidated Statements of Cash Flows to the Consolidated Balance Sheets:
Total cash, cash equivalents and restricted cash	$ 4,513,493	$ 3,994,454