Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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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.

+ Details

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- Definition

Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Details

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Bonds and Notes Payable - Bonds and Notes Payable Asset-backed Securitizations (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jun. 26, 2015
Asset-backed security [Member]
Debt Instrument [Line Items]
Total original principal amount	$ 1,473,790,000
Bond discount	(2,002,000)
Issue price	1,471,788,000
NSLT 2017-1 [Member] \| Asset-backed security [Member]
Debt Instrument [Line Items]
Total original principal amount	535,000,000
Bond discount	0
Issue price	535,000,000
NSLT 2017-2 [Member] \| Asset-backed security [Member]
Debt Instrument [Line Items]
Total original principal amount	399,390,000
Bond discount	(2,002,000)
Issue price	397,388,000
NSLT 2017-3 [Member] \| Asset-backed security [Member]
Debt Instrument [Line Items]
Total original principal amount	539,400,000
Bond discount	0
Issue price	$ 539,400,000
Asset-backed Securities [Member]
Debt Instrument [Line Items]
Total original principal amount		$ 651,960,000
Asset-backed Securities [Member] \| Class A [Member]
Debt Instrument [Line Items]
Total original principal amount		629,960,000
Bond discount		(609,000)
Issue price		629,351,000
Asset-backed Securities [Member] \| Class B [Member]
Debt Instrument [Line Items]
Total original principal amount		22,000,000
Bond discount		(285,000)
Issue price		21,715,000
Asset-backed Securities [Member] \| FFELP 2016-1 Securitization [Member]
Debt Instrument [Line Items]
Total original principal amount		426,000,000
Asset-backed Securities [Member] \| FFELP 2016-1 Securitization [Member] \| Class A [Member]
Debt Instrument [Line Items]
Total original principal amount		426,000,000
Bond discount		0
Issue price		426,000,000
Asset-backed Securities [Member] \| Private Education Loan 2016-A Securitization [Member]
Debt Instrument [Line Items]
Total original principal amount		225,960,000
Aggregate principal amount			$ 275,000,000.0
Asset-backed Securities [Member] \| Private Education Loan 2016-A Securitization [Member] \| Private Education Loan 2016-A Securitization Class A-1A [Member]
Debt Instrument [Line Items]
Total original principal amount		112,582,000
Asset-backed Securities [Member] \| Private Education Loan 2016-A Securitization [Member] \| Private Education Loan 2016-A Securitization Class A-1B [Member]
Debt Instrument [Line Items]
Total original principal amount		$ 91,378,000
Variable interest rate basis		3.60%
Asset-backed Securities [Member] \| Private Education Loan 2016-A Securitization [Member] \| Class A [Member]
Debt Instrument [Line Items]
Total original principal amount		$ 203,960,000
Bond discount		(609,000)
Issue price		203,351,000
Asset-backed Securities [Member] \| Private Education Loan 2016-A Securitization [Member] \| Class A [Member] \| Private Education Loan 2016-A Securitization Class A-1A [Member]
Debt Instrument [Line Items]
Total original principal amount		112,582,000
Bond discount		0
Issue price		112,582,000
Asset-backed Securities [Member] \| Private Education Loan 2016-A Securitization [Member] \| Class A [Member] \| Private Education Loan 2016-A Securitization Class A-1B [Member]
Debt Instrument [Line Items]
Total original principal amount		91,378,000
Bond discount		(609,000)
Issue price		90,769,000
Asset-backed Securities [Member] \| Private Education Loan 2016-A Securitization [Member] \| Class B [Member]
Debt Instrument [Line Items]
Total original principal amount		22,000,000
Bond discount		(285,000)
Issue price		$ 21,715,000
Variable interest rate basis		5.35%
London Interbank Offered Rate (LIBOR) [Member] \| NSLT 2017-1 [Member] \| Asset-backed security [Member]
Debt Instrument [Line Items]
Variable interest rate basis	0.78%
London Interbank Offered Rate (LIBOR) [Member] \| NSLT 2017-2 [Member] \| Asset-backed security [Member]
Debt Instrument [Line Items]
Variable interest rate basis	0.77%
London Interbank Offered Rate (LIBOR) [Member] \| NSLT 2017-3 [Member] \| Asset-backed security [Member]
Debt Instrument [Line Items]
Variable interest rate basis	0.85%
London Interbank Offered Rate (LIBOR) [Member] \| Asset-backed Securities [Member] \| FFELP 2016-1 Securitization [Member]
Debt Instrument [Line Items]
Variable interest rate basis		0.80%
London Interbank Offered Rate (LIBOR) [Member] \| Asset-backed Securities [Member] \| Private Education Loan 2016-A Securitization [Member] \| Private Education Loan 2016-A Securitization Class A-1A [Member]
Debt Instrument [Line Items]
Variable interest rate basis		1.75%