Borrowings - Summary of Exposure Related To Unconsolidated VIEs (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Estimated Fair Value	$ 2,115,885	$ 1,996,634
Total Exposure	19,367	110,044	$ 29,707	$ 2,481
Private Education Loan securitization \| Variable Interest Entity, Not Primary Beneficiary
Debt Instrument [Line Items]
Estimated Fair Value	199,135	68,908
Equity Interests	30,594	16,923
Total Exposure	$ 229,729	$ 85,831

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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