Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Student Loans Earning Fixed Rate Floor Income

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- Definition

Weighted Average Variable Conversion Rate

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- Definition

Average fixed interest rate related to the group of interest rate derivatives.

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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.

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- Definition

Fixed interest rate that will be received or paid upon exercise of the interest rate swaption contract.

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- Definition

The increase (decrease) during the reporting period in the aggregate value of financial instruments used in operating activities, including trading securities, risk management instruments, and other short-term trading instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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Derivative Financial Instruments - Interest Rate Swaps, Floor Income Hedge (Details) - USD ($) $ in Thousands		12 Months Ended
	Aug. 20, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Payments to enter into derivative instruments		$ (929)	$ 0	$ (2,936)
Swaption [Member]
Derivative [Line Items]
Notional amount		$ 250,000
Payments to enter into derivative instruments	$ (9,100)
Derivative, swaption interest rate		3.30%
Fixed Rate Floor Income [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Student loan assets, fixed floor income		$ 4,800,000	$ 8,400,000
Variable conversion rate		3.17%	2.42%
Notional amount		$ 7,300,000	$ 6,950,000
Weighted average fixed rate paid by the Company		1.21%	1.02%
Fixed Rate Floor Income [Member] \| Maturity 2017 [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount		$ 0	$ 750,000
Weighted average fixed rate paid by the Company		0.00%	0.99%
Fixed Rate Floor Income [Member] \| Maturity 2018 [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount		$ 1,350,000	$ 1,350,000
Weighted average fixed rate paid by the Company		1.07%	1.07%
Fixed Rate Floor Income [Member] \| Maturity 2019 [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount		$ 3,250,000	$ 3,250,000
Weighted average fixed rate paid by the Company		0.97%	0.97%
Fixed Rate Floor Income [Member] \| Maturity 2020 [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount		$ 1,500,000	$ 1,500,000
Weighted average fixed rate paid by the Company		1.01%	1.01%
Fixed Rate Floor Income [Member] \| Maturity 2023 [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount		$ 750,000
Weighted average fixed rate paid by the Company		2.28%
Fixed Rate Floor Income [Member] \| Maturity 2024 [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount		$ 300,000
Weighted average fixed rate paid by the Company		2.28%
Fixed Rate Floor Income [Member] \| Maturity 2025 [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount		$ 100,000	$ 100,000
Weighted average fixed rate paid by the Company		2.32%	2.32%
Fixed Rate Floor Income [Member] \| Maturity 2027 [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount		$ 50,000
Weighted average fixed rate paid by the Company		2.32%