Borrowings - Secured Financing (Details) - USD ($)	1 Months Ended
	Mar. 31, 2023	Aug. 31, 2022	Dec. 31, 2022
Securities Financing Transaction [Line Items]
Total Issued	$ 579,000,000		$ 575,000,000
Total loans and accrued interest amount securitized at inception	644,573,000		$ 674,387,000
2022-C
Securities Financing Transaction [Line Items]
Total Issued		$ 575,000,000
Weighted Average Life (in years)		4 years 8 months 8 days
2022-C | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Securities Financing Transaction [Line Items]
Basis spread on variable rate		1.76%
2023-A
Securities Financing Transaction [Line Items]
Total Issued	$ 579,000,000
Weighted Average Life (in years)	5 years 21 days
Principal amount of collateral	$ 598,000,000
Capitalized interest	$ 41,000,000
2023-A | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Securities Financing Transaction [Line Items]
Basis spread on variable rate	1.53%
Private Education Loans Securitized in 2022
Securities Financing Transaction [Line Items]
Loans	$ 610,000,000
Principal amount of collateral	572,000,000
Capitalized interest	38,000,000
Private Education Loans Securitized In 2023
Securities Financing Transaction [Line Items]
Loans	639,000,000
Principal amount of collateral	598,000,000
Capitalized interest	$ 41,000,000