Borrowings - Financing VIEs (Details) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Debt Outstanding
Short Term	$ 710,005,000	$ 0
Long Term	593,687,000	0
Total	1,303,692,000	0
Carrying Amount of Assets Securing Debt Outstanding
Restricted Cash	25,605,000	4,804,000
Other Assets	77,980,000	$ 64,757,000
Private Education Loan securitization
Debt Outstanding
Short Term	0
Long Term	593,687,000
Total	593,687,000
ABCP borrowings
Debt Outstanding
Short Term	710,005,000
Long Term	0
Total	710,005,000
Variable Interest Entity, Primary Beneficiary
Debt Outstanding
Short Term	710,005,000
Long Term	593,687,000
Total	1,303,692,000
Carrying Amount of Assets Securing Debt Outstanding
Loans	1,593,894,000
Restricted Cash	18,205,000
Other Assets	104,014,000
Total	1,716,113,000
Variable Interest Entity, Primary Beneficiary | Private Education Loan securitization
Debt Outstanding
Short Term	0
Long Term	593,687,000
Total	593,687,000
Carrying Amount of Assets Securing Debt Outstanding
Loans	692,379,000
Restricted Cash	8,135,000
Other Assets	49,717,000
Total	750,231,000
Variable Interest Entity, Primary Beneficiary | ABCP borrowings
Debt Outstanding
Short Term	710,005,000
Long Term	0
Total	710,005,000
Carrying Amount of Assets Securing Debt Outstanding
Loans	901,515,000
Restricted Cash	10,070,000
Other Assets	54,297,000
Total	$ 965,882,000