Borrowings - Summary of Exposure Related To Unconsolidated VIEs (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Estimated Fair Value	$ 2,271,108	$ 2,411,622
Total Exposure	32,034	112,962	$ 32,720	$ 124,924
Variable Interest Entity, Not Primary Beneficiary | Private Education Loan term securitizations
Debt Instrument [Line Items]
Estimated Fair Value	521,263	423,327
Equity Interests	58,166	54,481
Total Exposure	$ 579,429	$ 477,808