Borrowings - Company Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Secured borrowings:
Short-Term	$ 0	$ 0
Long-Term	5,235,114	5,930,990
Total	5,235,114	5,930,990
Unsecured borrowings
Secured borrowings:
Short-Term	0	0
Long-Term	988,986	986,138
Total	988,986	986,138
Secured borrowings
Secured borrowings:
Short-Term	0	0
Long-Term	4,246,128	4,944,852
Total	4,246,128	4,944,852
Secured borrowings | Private Education Loan term securitizations:
Secured borrowings:
Short-Term	0	0
Long-Term	4,246,128	4,944,852
Total	4,246,128	4,944,852
Secured borrowings | Secured Borrowing Facility
Secured borrowings:
Short-Term	0	0
Long-Term	0	0
Total	0	0
Secured borrowings | Fixed-rate | Private Education Loan term securitizations:
Secured borrowings:
Short-Term	0	0
Long-Term	3,462,363	3,897,996
Total	3,462,363	3,897,996
Secured borrowings | Variable-rate | Private Education Loan term securitizations:
Secured borrowings:
Short-Term	0	0
Long-Term	783,765	1,046,856
Total	$ 783,765	$ 1,046,856