Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
Percentage of Private Education Loans related to borrowers in school, grace or deferment	27.00%	25.00%
Interest rate offered to borrowers facing financial difficulty	4.00%
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
Percentage of loans granted forbearance (as a percentage)	48.00%	50.00%
Personal loans held for investment	$ 21,695,851	$ 24,667,792
Percentage reimbursement on all qualifying default claims period two (as a percentage)	97.00%
Percentage reimbursement on all qualifying default claims period one (as a percentage)	98.00%
Percentage reimbursement on all qualifying default claims period three (as a percentage)	100.00%
Variable rate	105.00%
Personal Loans
Financing Receivable, Impaired [Line Items]
Personal loans held for investment	$ 747,444	$ 983,643