Loans Held for Investment - Student Loan Portfolio by Program (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Private Education Loans	$ 15,654,854	$ 14,251,675
Deferred origination costs	46,692	44,206
Allowance for loan losses	(185,103)	(182,472)
Total Private Education Loans, net	15,516,443	14,113,409
FFELP Loans	989,393	1,010,908
Unamortized acquisition costs, net	2,855	2,941
Allowance for loan losses	(1,637)	(2,171)
Total FFELP Loans, net	990,611	1,011,678
Personal Loans	55,502	12,893
Allowance for loan losses	(346)	(58)
Total Personal Loans, net	55,156	12,835
Loans held for investment, net	$ 16,562,210	$ 15,137,922

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=65884687&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