Borrowings - Financing VIEs (Details) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Debt Outstanding
Short Term	$ 0	$ 500,175,000
Long Term	1,038,029,000	579,101,000
Total	1,038,029,000	1,079,276,000
Carrying Amount of Assets Securing Debt Outstanding
Restricted Cash	34,297,000	27,980,000
Other Assets	80,239,000	57,227,000
Private Education Loan securitization
Debt Outstanding
Short Term	0	0
Long Term	1,038,029,000	579,101,000
Total	1,038,029,000	579,101,000
ABCP Facility
Debt Outstanding
Short Term	0	500,175,000
Long Term	0	0
Total	0	500,175,000
Variable Interest Entity, Primary Beneficiary
Debt Outstanding
Short Term	0	500,175,000
Long Term	1,038,029,000	579,101,000
Total	1,038,029,000	1,079,276,000
Carrying Amount of Assets Securing Debt Outstanding
Loans	1,237,676,000	1,610,985,000
Restricted Cash	29,123,000	22,439,000
Other Assets	84,294,000	103,661,000
Total	1,351,093,000	1,737,085,000
Variable Interest Entity, Primary Beneficiary | Private Education Loan securitization
Debt Outstanding
Short Term	0	0
Long Term	1,038,029,000	579,101,000
Total	1,038,029,000	579,101,000
Carrying Amount of Assets Securing Debt Outstanding
Loans	1,237,676,000	687,298,000
Restricted Cash	29,123,000	9,996,000
Other Assets	84,294,000	45,566,000
Total	1,351,093,000	742,860,000
Variable Interest Entity, Primary Beneficiary | ABCP Facility
Debt Outstanding
Short Term	0	500,175,000
Long Term	0	0
Total	0	500,175,000
Carrying Amount of Assets Securing Debt Outstanding
Loans	0	923,687,000
Restricted Cash	0	12,443,000
Other Assets	0	58,095,000
Total	$ 0	$ 994,225,000