Borrowings - Secured Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Secured borrowings:
Short-Term	$ 500,175
Long-Term	579,101	$ 0
Total	1,079,276
Private Education Loan term securitizations
Secured borrowings:
Short-Term	0
Long-Term	579,101
Total	579,101
ABCP borrowings
Secured borrowings:
Short-Term	500,175
Long-Term	0
Total	$ 500,175