Borrowings - Financing VIEs (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Debt Outstanding
Short Term	$ 350,000	$ 500,175
Long Term	1,577,689	579,101
Total	1,927,689	1,079,276
Carrying Amount of Assets Securing Debt Outstanding
Restricted Cash	38,256	27,980
Other Assets	62,545	57,227
Private Education Loan securitization
Debt Outstanding
Short Term	0	0
Long Term	1,577,689	579,101
Total	1,577,689	579,101
ABCP Facility
Debt Outstanding
Short Term	350,000	500,175
Long Term	0	0
Total	350,000	500,175
Variable Interest Entity, Primary Beneficiary
Debt Outstanding
Short Term	350,000	500,175
Long Term	1,577,689	579,101
Total	1,927,689	1,079,276
Carrying Amount of Assets Securing Debt Outstanding
Loans	2,329,852	1,610,985
Restricted Cash	34,279	22,439
Other Assets	163,309	103,661
Total	2,527,440	1,737,085
Variable Interest Entity, Primary Beneficiary | Private Education Loan securitization
Debt Outstanding
Short Term	0	0
Long Term	1,577,689	579,101
Total	1,577,689	579,101
Carrying Amount of Assets Securing Debt Outstanding
Loans	1,901,146	687,298
Restricted Cash	27,597	9,996
Other Assets	133,896	45,566
Total	2,062,639	742,860
Variable Interest Entity, Primary Beneficiary | ABCP Facility
Debt Outstanding
Short Term	350,000	500,175
Long Term	0	0
Total	350,000	500,175
Carrying Amount of Assets Securing Debt Outstanding
Loans	428,706	923,687
Restricted Cash	6,682	12,443
Other Assets	29,413	58,095
Total	$ 464,801	$ 994,225