Borrowings - Financing VIEs (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Debt Outstanding
Short Term	$ 526,500	$ 500,175
Long Term	558,513	579,101
Total	1,085,013	1,079,276
Carrying Amount of Assets Securing Debt Outstanding
Restricted Cash	24,612	27,980
Other Assets(1)	70,493	55,482
Private Education Loan securitization
Debt Outstanding
Short Term	0	0
Long Term	558,513	579,101
Total	558,513	579,101
ABCP Facility
Debt Outstanding
Short Term	526,500	500,175
Long Term	0	0
Total	526,500	500,175
Variable Interest Entity, Primary Beneficiary
Debt Outstanding
Short Term	526,500	500,175
Long Term	558,513	579,101
Total	1,085,013	1,079,276
Carrying Amount of Assets Securing Debt Outstanding
Loans	1,573,652	1,610,985
Restricted Cash	25,848	22,439
Other Assets(1)	138,018	103,661
Total	1,737,518	1,737,085
Variable Interest Entity, Primary Beneficiary | Private Education Loan securitization
Debt Outstanding
Short Term	0	0
Long Term	558,513	579,101
Total	558,513	579,101
Carrying Amount of Assets Securing Debt Outstanding
Loans	671,603	687,298
Restricted Cash	10,281	9,996
Other Assets(1)	46,305	45,566
Total	728,189	742,860
Variable Interest Entity, Primary Beneficiary | ABCP Facility
Debt Outstanding
Short Term	526,500	500,175
Long Term	0	0
Total	526,500	500,175
Carrying Amount of Assets Securing Debt Outstanding
Loans	902,049	923,687
Restricted Cash	15,567	12,443
Other Assets(1)	91,713	58,095
Total	$ 1,009,329	$ 994,225