Derivative Financial Instruments - Derivative Impact on Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	$ 166	$ 744	$ 746	$ 1,489
Change in fair value	$ 3,686	$ (3,866)	$ 5,273	$ (10,190)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Derivative market value adjustments and derivative settlements, net	Derivative market value adjustments and derivative settlements, net	Derivative market value adjustments and derivative settlements, net	Derivative market value adjustments and derivative settlements, net
Derivative Instruments, Gain (Loss) by Income Statement Location [Axis]: nni:DerivativeMarketValueAdjustmentsAndDerivativeSettlementsNet
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	$ 166	$ 744	$ 746	$ 1,489
Derivative market value adjustments and derivative settlements, net - income (expense)	3,852	(3,122)	6,019	(8,701)
Basis swaps
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value	(150)	(143)	(298)	(281)
Basis swaps \| Derivative Instruments, Gain (Loss) by Income Statement Location [Axis]: nni:DerivativeMarketValueAdjustmentsAndDerivativeSettlementsNet
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	154	154	307	307
Interest rate swaps - floor income hedges
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value	2,108	(2,022)	3,750	(5,680)
Interest rate swaps - floor income hedges \| Derivative Instruments, Gain (Loss) by Income Statement Location [Axis]: nni:DerivativeMarketValueAdjustmentsAndDerivativeSettlementsNet
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	(65)	427	(114)	855
Interest rate swaps - Nelnet Bank intercompany deposits
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value	1,714	(1,701)	2,714	(4,229)
Interest rate swaps - Nelnet Bank intercompany deposits \| Derivative Instruments, Gain (Loss) by Income Statement Location [Axis]: nni:DerivativeMarketValueAdjustmentsAndDerivativeSettlementsNet
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	77	163	116	327
Other derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value	14	0	(893)	0
Other derivative instruments \| Derivative Instruments, Gain (Loss) by Income Statement Location [Axis]: nni:DerivativeMarketValueAdjustmentsAndDerivativeSettlementsNet
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	$ 0	$ 0	$ 437	$ 0

derivative settlements

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Indicates line item in statement of income or comprehensive income that includes gain (loss) from derivative.

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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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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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