Loans Held for Investment - Student Loan Portfolio by Program (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Private Education Loans	$ 12,111,870	$ 10,596,437
Deferred origination costs	31,772	27,884
Allowance for loan losses	(122,620)	(108,816)
Total Private Education Loans, net	12,021,022	10,515,505
FFELP Loans	1,088,026	1,115,663
Unamortized acquisition costs, net	3,006	3,114
Allowance for loan losses	(3,629)	(3,691)
Total FFELP Loans, net	1,087,403	1,115,086
Loans held for investment, net	$ 13,108,425	$ 11,630,591

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