Arrangements with Navient Corporation Arrangements with Navient Corporation (Details) - USD ($)		12 Months Ended
	Apr. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Non-compete period	5 years
Deferred taxes	$ 283,000,000	$ 9,180,000	$ 81,588,000
Remaining amount of indemnification		116,000,000
Deferred tax asset discount	$ 27,000,000	116,000,000
Remaining balance of indemnification receivable in connection with the spin-off		28,000,000
Private education loans		$ 14,251,675,000	10,596,437,000
Minimum days past due for spin off loan purchase		90 days
Period of hardship forbearance		6 months
Private education loans		$ 14,113,409,000	10,515,505,000
Interest income from third party		300,000	600,000	$ 5,700,000
Gain (Loss) resulting from loans sold		0	0	35,800,000
Write-down to fair value for loans sold to third party		6,000,000	7,600,000	53,500,000
Split Loans
Related Party Transaction [Line Items]
Private education loans		67,000,000
Participated loans
Related Party Transaction [Line Items]
Loans sold to third party		15,700,000	$ 27,000,000	$ 804,700,000
FFELP Loans
Related Party Transaction [Line Items]
Private education loans		$ 67,000,000
Minimum
Related Party Transaction [Line Items]
Agreements with Navient, period of term (or less)	2 years
Maximum
Related Party Transaction [Line Items]
Agreements with Navient, period of term (or less)	3 years