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Investments and Notes Receivable - Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	$ 47,419
Amortized cost, after 1 year through 5 years	86,614
Amortized cost, after 5 years through 10 years	118,992
Amortized cost, after 10 years	834,198
Amortized cost	1,087,223
Available-for-sale asset-backed securities, at fair value
Fair value, 1 year or less	47,815
Fair value, after 1 year through 5 years	87,100
Fair value, after 5 years through 10 years	119,480
Fair value, after 10 years	831,431
Total	1,085,826
Held to maturity investments
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	2,759
Amortized cost, after 5 years through 10 years	1,136
Amortized cost, after 10 years	206,879
Total	210,774	$ 162,738
Held to maturity investments, at fair value
Fair value, 1 year or less	0
Fair value, after 1 year through 5 years	2,827
Fair value, after 5 years through 10 years	1,160
Fair value, after 10 years	212,177
Total	216,164
Beneficial Interest In Securitization [Abstract]
Amortized cost, after 1 year through 5 years	0
Amortized cost, 1 year or less	0
Amortized cost, after 5 years through 10 years	0
Amortized cost, after 10 years	0
Beneficial interest in securitizations	213,809	225,079
Fair value
Fair value, 1 year or less	0
Fair value, after 1 year through 5 years	0
Fair value, after 5 years through 10 years	0
Fair value, after 10 years	0
Beneficial interest in loan securitizations	229,510
Asset-Backed Securities, Available-For-Sale, Federal Family Education Loan Program (FFELP) Loans, Restricted Investments
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	10,253
Amortized cost, after 5 years through 10 years	17,863
Amortized cost, after 10 years	70,798
Amortized cost	98,914
Asset-Backed Securities, Available-For-Sale, Non-Nelnet Bank
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	24,096
Amortized cost, after 5 years through 10 years	32,676
Amortized cost, after 10 years	500,368
Amortized cost	557,140	611,956
Available-for-sale asset-backed securities, at fair value
Fair value, 1 year or less	0
Fair value, after 1 year through 5 years	24,397
Fair value, after 5 years through 10 years	32,924
Fair value, after 10 years	492,182
Total	549,503	584,293
Asset-Backed Securities, Available-For-Sale, Federal Family Education Loan Program (FFELP) Loans, Non-Nelnet Bank
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	13,743
Amortized cost, after 5 years through 10 years	5,332
Amortized cost, after 10 years	169,311
Amortized cost	188,386	271,479
Available-for-sale asset-backed securities, at fair value
Total	193,294	270,969
Asset-Backed Securities, Available-For-Sale, Private Education Loans, Non-Nelnet Bank
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	0
Amortized cost, after 5 years through 10 years	0
Amortized cost, after 10 years	237,288
Amortized cost	237,288	281,791
Available-for-sale asset-backed securities, at fair value
Total	219,170	252,917
Asset-Backed Securities, Available-For-Sale, Other, Non-Nelnet Bank
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	100
Amortized cost, after 5 years through 10 years	9,481
Amortized cost, after 10 years	22,971
Amortized cost	32,552	41,693
Available-for-sale asset-backed securities, at fair value
Total	35,052	42,438
Asset-Backed Securities, Available-For-Sale, Nelnet Bank
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	47,419
Amortized cost, after 1 year through 5 years	62,518
Amortized cost, after 5 years through 10 years	86,316
Amortized cost, after 10 years	333,830
Amortized cost	530,083	370,922
Available-for-sale asset-backed securities, at fair value
Fair value, 1 year or less	47,815
Fair value, after 1 year through 5 years	62,703
Fair value, after 5 years through 10 years	86,556
Fair value, after 10 years	339,249
Total	536,323	371,610
Asset-Backed Securities, Available-For-Sale, Federal Family Education Loan Program (FFELP) Loans, Nelnet Bank
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	47,419
Amortized cost, after 1 year through 5 years	22,157
Amortized cost, after 5 years through 10 years	27,490
Amortized cost, after 10 years	134,477
Amortized cost	231,543	304,555
Available-for-sale asset-backed securities, at fair value
Total	237,333	306,757
Asset-Backed Securities, Available-For-Sale, Private Education Loans, Nelnet Bank
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	0
Amortized cost, after 5 years through 10 years	0
Amortized cost, after 10 years	1,596
Amortized cost	1,596	17,083
Available-for-sale asset-backed securities, at fair value
Total	1,596	17,093
Asset-Backed Securities, Available-For-Sale, Other, Nelnet Bank
Available-for-sale asset-backed securities
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	40,361
Amortized cost, after 5 years through 10 years	58,826
Amortized cost, after 10 years	197,757
Amortized cost	296,944	49,284
Available-for-sale asset-backed securities, at fair value
Total	297,394	47,760
Debt Securities, Held-To-Maturity, Non-Nelnet Bank
Held to maturity investments
Total	0	4,700
Held-To-Maturity Investments, Nelnet Bank
Held to maturity investments
Total	210,774	158,038
Asset-Backed Securities, Held-To-Maturity, Federal Family Education Loan Program (FFELP) Loans, Nelnet Bank
Held to maturity investments
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	2,759
Amortized cost, after 5 years through 10 years	1,136
Amortized cost, after 10 years	199,544
Total	203,439	149,938
Debt Securities, Held-To-Maturity, Other, Nelnet Bank
Held to maturity investments
Amortized cost, 1 year or less	0
Amortized cost, after 1 year through 5 years	0
Amortized cost, after 5 years through 10 years	0
Amortized cost, after 10 years	7,335
Total	$ 7,335	$ 8,100

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