Arrangements with Navient Corporation Arrangements with Navient Corporation (Details) - USD ($)		12 Months Ended
	Apr. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Agreements with Navient, period of term (or less)	2 years
Non-compete period	5 years
Deferred taxes	$ 283,000,000	$ 81,588,000	$ 158,216,000
Remaining amount of indemnification		170,000,000
Deferred tax asset discount		16,000,000
FDIC civil monetary penalties		3,300,000
Contingency refund		$ 30,000,000
Minimum days past due for spin off loan purchase		90 days
Period of hardship forbearance		6 months
Private education loans		$ 10,515,505,000	8,246,647,000
Interest income from related party		600,000	5,700,000	$ 67,000,000
Gain (Loss) resulting from loans sold		0	35,800,000	196,600,000
Write-down to fair value for loans sold to related party		7,600,000	53,500,000	68,400,000
Participated loans
Related Party Transaction [Line Items]
Loans sold to related party		27,000,000	$ 804,700,000	$ 2,415,800,000
Split Loans
Related Party Transaction [Line Items]
Private education loans		$ 89,000,000