Significant Accounting Policies - Troubled Debt Restructurings and Allowance for Credit Loss Narrative (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Private Education Loans related to borrowers in school, grace or deferment		25.00%	24.00%
Period of forbearance period to be classified as TDR		3 months
Period of forbearance		24 months
Period after grace period for forbearance allowance for loans		9 months
Forbearance period after grace period for loans		6 months
Monthly payment that is smaller than the interest accrued on the loan in that month		$ 25
Financing receivable allowance for credit loss, transfer to held-to-sale	$ 2,400,000
Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable allowance for credit loss, transfer to held-to-sale		$ 2,400,000