Loans Held for Investment - Student Loan Portfolio by Program (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
FFELP Loans	$ 846,487	$ 927,660
Deferred origination costs and unamortized premium/ (discount)	2,379	2,631
Allowance for loan losses	(977)	(1,132)
Total FFELP Loans, net	847,889	929,159
Loans held for investment, net	22,270,919	18,567,641
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, before Fees, Gross	20,504,465	17,432,167
Deferred origination costs and unamortized premium/ (discount)	68,321	56,378
Allowance for loan losses	(277,943)	(243,715)
Total Private Education Loans, net	20,294,843	17,244,830
Personal Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred origination costs and unamortized premium/ (discount)	297	0
Personal Loans (fixed-rate)	1,190,091	400,280
Allowance for loan losses	(62,201)	(6,628)
Total Personal Loans, net	1,128,187	393,652
Fixed Income Interest Rate \| Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, before Fees, Gross	6,759,019	4,000,447
Variable Income Interest Rate \| Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, before Fees, Gross	$ 13,745,446	$ 13,431,720

Allowance for private education loans losses.

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- Definition

FFELP loan allowance for losses.

+ References

No definition available.

+ Details

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- Definition

FFELP loans.

+ References

No definition available.

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- Definition

FFELP loans, net.

+ References

No definition available.

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- Definition

Ffelp origination fees, net

+ References

No definition available.

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- Definition

Loans and Leases Receivable, Allowance for Loan Losses

+ References

No definition available.

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- Definition

Loans and Leases Receivable, Personal Loans

+ References

No definition available.

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Loans and Leases Receivable, Personal Loans, Total

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No definition available.

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- Definition

Private education loans net.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount, before allowance and fees, of loans and leases receivable. Excludes loans and leases covered under loss sharing agreements.

+ References

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
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-Paragraph 1
-Subparagraph (SX 210.9-03.7)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

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