Delinquencies as a percentage of loans in repayment.

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Loan status forbearance recorded investment.

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Loan status in school grace and deferment recorded investment.

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Loans in forbearance as a percentage of loans in repayment and forbearance.

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Total loans in repayment.

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Loans in repayment and percentage of each status.

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Loans in repayment current in percentage.

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Total loans in repayment, in percentage.

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Percentage of loans in repayment.

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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.

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Percentage of financing receivable balance that is past due.

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Financing receivables that are current.

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Recorded Investment in financing receivables that are past due at the balance sheet date.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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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.

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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.

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Allowance for Loan Losses - Age Analysis of Past Due Loans Delinquencies (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Loans in repayment and percentage of each status:
Private Education Loans allowance for losses	$ (328,974)	$ (295,277)	$ (251,475)	$ (229,919)	$ (207,448)	$ (184,701)
Loans held for investment, net	21,978,903		18,567,641
Private Education Loans
Loans in repayment and percentage of each status:
Private Education Loans deferred origination costs	65,499		56,378
Total Private Education Loans, gross	20,239,991		17,432,167
Private Education Loans allowance for losses	(274,684)		(243,715)
Loans held for investment, net	20,030,806		17,244,830
Private Education Loans \| Consumer Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in-school/grace/deferment	5,936,033		4,757,732
Loans in forbearance	488,543		468,402
Loans in repayment and percentage of each status:
Loans current	$ 13,492,029		$ 11,911,128
Loans current (as a percentage)	97.70%		97.60%
Total TDR loans in repayment	$ 13,815,415		$ 12,206,033
Total TDR loans in repayment (as a percentage)	100.00%		100.00%
Private Education Loans deferred origination costs	$ 65,499		$ 56,378
Total Private Education Loans, gross	20,305,490		17,488,545
Total Private Education Loans, gross	20,239,991		17,432,167
Private Education Loans allowance for losses	(274,684)		(243,715)
Loans held for investment, net	$ 20,030,806		$ 17,244,830
Percentage of Private Education Loans in repayment	68.30%		70.00%
Delinquencies as a percentage of Private Education Loans in repayment	2.30%		2.40%
Loans in forbearance as a percentage of Private Education Loans in repayment and forbearance	3.40%		3.70%
Private Education Loans \| Consumer Portfolio Segment \| Loans delinquent 31-60 days
Loans in repayment and percentage of each status:
Loans delinquent	$ 198,987		$ 179,002
Loans delinquent (as a percentage)	1.40%		1.50%
Private Education Loans \| Consumer Portfolio Segment \| Loans delinquent 61-90 days
Loans in repayment and percentage of each status:
Loans delinquent	$ 82,358		$ 78,292
Loans delinquent (as a percentage)	0.60%		0.60%
Private Education Loans \| Consumer Portfolio Segment \| Loans delinquent, greater than 90 days
Loans in repayment and percentage of each status:
Loans delinquent	$ 42,041		$ 37,611
Loans delinquent (as a percentage)	0.30%		0.30%
Personal Loans
Loans in repayment and percentage of each status:
Private Education Loans deferred origination costs	$ 164		$ 0
Total Private Education Loans, gross	1,133,005		400,280
Private Education Loans allowance for losses	(53,210)		(6,628)
Loans held for investment, net	1,079,959		393,652
Personal Loans \| Consumer Portfolio Segment
Loans in repayment and percentage of each status:
Loans current	$ 1,123,597		$ 398,988
Loans current (as a percentage)	99.20%		99.70%
Total TDR loans in repayment	$ 1,133,005		$ 400,280
Total TDR loans in repayment (as a percentage)	100.00%		100.00%
Private Education Loans deferred origination costs	$ 164		$ 0
Total Private Education Loans, gross	1,133,169		400,280
Total Private Education Loans, gross	1,133,005		400,280
Private Education Loans allowance for losses	(53,210)		(6,628)
Loans held for investment, net	$ 1,079,959		$ 393,652
Delinquencies as a percentage of Private Education Loans in repayment	0.80%		0.30%
Personal Loans \| Consumer Portfolio Segment \| Loans delinquent 31-60 days
Loans in repayment and percentage of each status:
Loans delinquent	$ 4,321		$ 761
Loans delinquent (as a percentage)	0.40%		0.20%
Personal Loans \| Consumer Portfolio Segment \| Loans delinquent 61-90 days
Loans in repayment and percentage of each status:
Loans delinquent	$ 2,804		$ 340
Loans delinquent (as a percentage)	0.20%		0.10%
Personal Loans \| Consumer Portfolio Segment \| Loans delinquent, greater than 90 days
Loans in repayment and percentage of each status:
Loans delinquent	$ 2,283		$ 191
Loans delinquent (as a percentage)	0.20%		0.00%