Loans Held for Investment - Student Loan Portfolio by Program (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Receivables [Abstract]
Private Education Loans	$ 10,596,437	$ 8,311,376
Deferred origination costs	27,884	13,845
Allowance for loan losses	(108,816)	(78,574)
Total Private Education Loans, net	10,515,505	8,246,647
FFELP Loans	1,115,663	1,264,807
Unamortized acquisition costs, net	3,114	3,600
Allowance for loan losses	(3,691)	(5,268)
Total FFELP Loans, net	1,115,086	1,263,139
Loans held for investment, net	$ 11,630,591	$ 9,509,786

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Name:	us-gaap_LoansAndLeasesReceivableNetReportedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant