Borrowings - Variable Interest Entity (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Secured borrowings:
Short-Term	$ 500,175
Long-term borrowings	579,101	$ 0
Total	1,079,276
Restricted cash and investments	27,980	4,804
Other assets	55,482	$ 64,757
Private Education Loan term securitizations
Secured borrowings:
Short-Term	0
Long-term borrowings	579,101
Total	579,101
ABCP borrowings
Secured borrowings:
Short-Term	500,175
Long-term borrowings	0
Total	500,175
Variable Interest Entity, Primary Beneficiary
Secured borrowings:
Short-Term	500,175
Long-term borrowings	579,101
Total	1,079,276
Loans	1,610,985
Restricted cash and investments	22,439
Other assets	103,661
Total	1,737,085
Variable Interest Entity, Primary Beneficiary | Private Education Loan term securitizations
Secured borrowings:
Short-Term	0
Long-term borrowings	579,101
Total	579,101
Loans	687,298
Restricted cash and investments	9,996
Other assets	45,566
Total	742,860
Variable Interest Entity, Primary Beneficiary | ABCP borrowings
Secured borrowings:
Short-Term	500,175
Long-term borrowings	0
Total	500,175
Loans	923,687
Restricted cash and investments	12,443
Other assets	58,095
Total	$ 994,225