Borrowings - Summary of Exposure Related To Unconsolidated VIEs (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Estimated Fair Value	$ 2,022,605		$ 2,411,622
Total Exposure	91,959	$ 49,479	112,962	$ 113,847	$ 62,600	$ 124,924
Variable Interest Entity, Not Primary Beneficiary | Private Education Loan term securitizations
Debt Instrument [Line Items]
Estimated Fair Value	591,155		423,327
Equity Interests	54,840		54,481
Total Exposure	$ 645,995		$ 477,808