Borrowings - Summary of Exposure Related To Unconsolidated VIEs (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Estimated Fair Value	$ 2,311,062	$ 2,342,089
Total Exposure	32,720	124,924	$ 32,707	$ 72,713
Variable Interest Entity, Not Primary Beneficiary | Private Education Loan term securitizations
Debt Instrument [Line Items]
Estimated Fair Value	317,077	329,188
Equity Interests	51,342	50,786
Total Exposure	$ 368,419	$ 379,974