Borrowings - Summary of Exposure Related To Unconsolidated VIEs (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Estimated Fair Value	$ 2,372,846		$ 2,342,089
Total Exposure	62,600	$ 32,720	124,924	$ 113,525	$ 32,707	$ 72,713
Variable Interest Entity, Not Primary Beneficiary | Private Education Loan term securitizations
Debt Instrument [Line Items]
Estimated Fair Value	411,070		329,188
Equity Interests	52,146		50,786
Total Exposure	$ 463,216		$ 379,974