Borrowings - Company Borrowings (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Short Term	$ 526,500	$ 500,175
Long Term	558,513	579,101
Total	1,085,013	1,079,276
Private Education Loan securitization
Debt Instrument [Line Items]
Short Term	0	0
Long Term	558,513	579,101
Total	558,513	579,101
ABCP borrowings
Debt Instrument [Line Items]
Short Term	526,500	500,175
Long Term	0	0
Total	$ 526,500	$ 500,175