Borrowings - Summary of Exposure Related to Unconsolidated VIEs (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Estimated Fair Value	$ 1,933,226	$ 2,411,622
Liability for unfunded commitments	84,568	112,962	$ 124,924	$ 72,713
Variable Interest Entity, Not Primary Beneficiary | Private Education Loan term securitizations:
Debt Instrument [Line Items]
Estimated Fair Value	571,795	423,327
Equity Interests	53,262	54,481
Liability for unfunded commitments	$ 625,057	$ 477,808