CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income (loss)	$ 276,962	$ 308,466
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Provisions for credit losses	413,145	157,165
Income tax expense	90,817	90,097
Amortization of brokered deposit placement fee	10,128	7,625
Amortization of Secured Borrowing Facility upfront fee	1,346	559
Amortization of deferred loan origination costs and loan premium/(discounts), net	16,220	6,426
Net amortization of discount on investments	2,551	493
Unrealized gain on investments	(1,710)	0
(Increase) reduction in tax indemnification receivable	(567)	282
Depreciation of premises and equipment	7,677	6,968
Stock-based compensation expense	21,009	19,473
Unrealized gains on derivatives and hedging activities, net	(34,752)	(21,950)
Gains on sales of loans, net	(238,566)	0
Gain on sale of Upromise subsidiary, net	(11,331)	0
Other adjustments to net income, net	3,812	3,851
Changes in operating assets and liabilities:
Increase in accrued interest receivable	(464,291)	(478,886)
Increase in other interest-earning assets	(22,338)	(38,030)
Increase in other assets	(62,497)	(28,297)
Decrease in income taxes payable, net	(23,597)	(132,250)
(Decrease) increase in accrued interest payable	(11,912)	7,037
Decrease in Upromise member accounts due to sale	(193,840)	0
Increase in other liabilities	159,589	27,927
Total adjustments	(339,107)	(371,510)
Total net cash used in operating activities	(62,145)	(63,044)
Investing activities
Loans acquired and originated	(2,824,850)	(2,919,389)
Net proceeds from sales of loans held for investment	3,283,039	0
Proceeds from claim payments	17,308	21,356
Net decrease in loans held for investment	2,035,613	2,004,272
Purchases of available-for-sale securities	(1,556,084)	(160,317)
Proceeds from sales and maturities of available-for-sale securities	105,073	10,629
Proceeds from sale of Upromise subsidiary, net	16,922	0
Total net cash provided by (used in) investing activities	1,077,021	(1,043,449)
Financing activities
Brokered deposit placement fee	(3,305)	(15,380)
Net (decrease) increase in certificates of deposit	(1,059,731)	1,787,511
Net increase in other deposits	220,047	373,452
Borrowings collateralized by loans in securitization trusts - issued	633,305	1,105,594
Borrowings collateralized by loans in securitization trusts - repaid	(541,365)	(530,765)
Repayment of borrowings under Secured Borrowing Facility	(289,230)	0
Fees paid on Secured Borrowing Facility	(3,251)	(1,116)
Common stock dividends paid	(23,844)	(25,824)
Preferred stock dividends paid	(5,942)	(8,799)
Common stock repurchased	(558,167)	(120,120)
Net cash (used in) provided by financing activities	(1,631,483)	2,564,553
Net (decrease) increase in cash, cash equivalents and restricted cash	(616,607)	1,458,060
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	5,104,153	4,139,955
Cash disbursements made for:
Interest	304,119	323,278
Income taxes paid	27,661	132,036
Income taxes refunded	(4,016)	(718)
Reconciliation of the Consolidated Statements of Cash Flows to the Consolidated Balance Sheets:
Total cash, cash equivalents and restricted cash	$ 5,104,153	$ 4,139,955