Segment Reporting (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) operating_segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | operating_segment									4
Total interest income									$ 770,426	$ 760,746	$ 734,109
Interest expense									465,188	388,183	302,210
Net interest income	$ 73,235	$ 75,237	$ 79,842	$ 76,925	$ 78,960	$ 99,795	$ 92,200	$ 101,609	305,238	372,563	431,899
Less provision for loan losses	3,750	6,700	3,000	1,000	3,000	6,000	2,000	2,500	14,450	13,500	10,150
Net interest income (loss) after provision for loan losses	69,485	68,537	76,842	75,925	75,960	93,795	90,200	99,109	290,788	359,063	421,749
Other income:
Loan systems and servicing revenue	55,921	55,950	56,899	54,229	53,764	54,350	54,402	52,330	223,000	214,846	239,858
Intersegment servicing revenue									0	0	0
Tuition payment processing, school information, and campus commerce revenue	32,457	35,450	34,224	43,620	30,519	33,071	30,483	38,657	145,751	132,730	120,365
Communications revenue	8,122	6,751	5,719	5,106	4,492	4,343	4,478	4,346	25,700	17,659	0
Enrollment services revenue					0	0	0	4,326	0	4,326	51,073
Other income	7,952	19,756	12,485	12,632	15,218	15,150	9,765	13,796	52,826	53,929	47,262
Gain on sale of loans and debt repurchases, net	(2,635)	116	442	4,980	5,720	2,160	0	101	2,902	7,981	5,153
Derivative settlements, net									667	(21,949)	(24,250)
Derivative market value and foreign currency transaction adjustments, net									(19,221)	71,744	28,651
Total other income									431,625	481,266	468,112
Operating expenses:
Salaries and benefits	81,201	74,193	74,628	71,863	68,017	63,743	60,923	63,242	301,885	255,924	247,914
Depreciation and amortization	11,854	10,051	9,038	8,598	9,116	8,994	8,183	7,640	39,541	33,933	26,343
Loan servicing fees	3,064	8,017	5,628	6,025	5,726	5,880	7,216	6,928	22,734	25,750	30,213
Cost to provide communications services	3,160	2,632	2,203	1,954	1,697	1,784	1,681	1,703	9,950	6,866	0
Cost to provide enrollment services										3,623	41,733
Other expenses	38,809	29,743	26,521	26,547	31,245	26,391	29,409	28,376	121,619	115,419	123,014
Intersegment expenses, net									0	0	0
Total operating expenses									495,729	441,515	469,217
Income (loss) before income taxes									226,684	398,814	420,644
Income tax (expense) benefit	5,486	(25,562)	(16,032)	(28,755)	(54,128)	(47,715)	(15,036)	(24,433)	(64,863)	(141,313)	(152,380)
Net income (loss)	45,714	43,535	24,651	47,920	98,931	84,363	26,178	48,029	161,821	257,501	268,264
Net loss (income) attributable to noncontrolling interests	2,386	2,768	4,086	2,106	(585)	(69)	(28)	(68)	11,345	(750)	(285)
Net income attributable to Nelnet, Inc.	48,100	$ 46,303	$ 28,737	$ 50,026	98,346	$ 84,294	$ 26,150	$ 47,961	173,166	256,751	267,979
Total assets	23,964,435				27,193,095				23,964,435	27,193,095	30,419,144
Operating Segments [Member] | Loan Systems and Servicing [Member]
Segment Reporting Information [Line Items]
Total interest income									513	111	49
Interest expense									3	0	0
Net interest income									510	111	49
Less provision for loan losses									0	0	0
Net interest income (loss) after provision for loan losses									510	111	49
Other income:
Loan systems and servicing revenue									223,000	214,846	239,858
Intersegment servicing revenue									41,674	45,381	50,354
Tuition payment processing, school information, and campus commerce revenue									0	0	0
Communications revenue									0	0
Enrollment services revenue										0	0
Other income									0	0	0
Gain on sale of loans and debt repurchases, net									0	0	0
Derivative settlements, net									0	0	0
Derivative market value and foreign currency transaction adjustments, net									0	0	0
Total other income									264,674	260,227	290,212
Operating expenses:
Salaries and benefits									156,256	132,072	134,635
Depreciation and amortization									2,864	1,980	1,931
Loan servicing fees									0	0	0
Cost to provide communications services									0	0
Cost to provide enrollment services										0	0
Other expenses									39,126	40,715	57,799
Intersegment expenses, net									31,871	24,204	29,706
Total operating expenses									230,117	198,971	224,071
Income (loss) before income taxes									35,067	61,367	66,190
Income tax (expense) benefit									(18,128)	(23,319)	(25,153)
Net income (loss)									16,939	38,048	41,037
Net loss (income) attributable to noncontrolling interests									12,640	0	20
Net income attributable to Nelnet, Inc.									29,579	38,048	41,057
Total assets	122,330				55,469				122,330	55,469	80,459
Operating Segments [Member] | Tuition Payment Processing and Campus Commerce [Member]
Segment Reporting Information [Line Items]
Total interest income									17	9	3
Interest expense									0	0	0
Net interest income									17	9	3
Less provision for loan losses									0	0	0
Net interest income (loss) after provision for loan losses									17	9	3
Other income:
Loan systems and servicing revenue									0	0	0
Intersegment servicing revenue									0	0	0
Tuition payment processing, school information, and campus commerce revenue									145,751	132,730	120,365
Communications revenue									0	0
Enrollment services revenue										0	0
Other income									0	0	(925)
Gain on sale of loans and debt repurchases, net									0	0	0
Derivative settlements, net									0	0	0
Derivative market value and foreign currency transaction adjustments, net									0	0	0
Total other income									145,751	132,730	119,440
Operating expenses:
Salaries and benefits									69,500	62,329	55,523
Depreciation and amortization									9,424	10,595	8,992
Loan servicing fees									0	0	0
Cost to provide communications services									0	0
Cost to provide enrollment services										0	0
Other expenses									19,138	18,486	15,161
Intersegment expenses, net									9,079	6,615	8,617
Total operating expenses									107,141	98,025	88,293
Income (loss) before income taxes									38,627	34,714	31,150
Income tax (expense) benefit									(14,678)	(13,191)	(11,838)
Net income (loss)									23,949	21,523	19,312
Net loss (income) attributable to noncontrolling interests									0	0	0
Net income attributable to Nelnet, Inc.									23,949	21,523	19,312
Total assets	250,351				230,283				250,351	230,283	229,615
Operating Segments [Member] | Communications [Member]
Segment Reporting Information [Line Items]
Total interest income									3	1	0
Interest expense									5,427	1,271	0
Net interest income									(5,424)	(1,270)	0
Less provision for loan losses									0	0	0
Net interest income (loss) after provision for loan losses									(5,424)	(1,270)	0
Other income:
Loan systems and servicing revenue									0	0	0
Intersegment servicing revenue									0	0	0
Tuition payment processing, school information, and campus commerce revenue									0	0	0
Communications revenue									25,700	17,659
Enrollment services revenue										0	0
Other income									0	0	0
Gain on sale of loans and debt repurchases, net									0	0	0
Derivative settlements, net									0	0	0
Derivative market value and foreign currency transaction adjustments, net									0	0	0
Total other income									25,700	17,659	0
Operating expenses:
Salaries and benefits									14,947	7,649	0
Depreciation and amortization									11,835	6,060	0
Loan servicing fees									0	0	0
Cost to provide communications services									9,950	6,866
Cost to provide enrollment services										0	0
Other expenses									8,074	4,370	0
Intersegment expenses, net									2,101	958	0
Total operating expenses									46,907	25,903	0
Income (loss) before income taxes									(26,631)	(9,514)	0
Income tax (expense) benefit									10,120	3,615	0
Net income (loss)									(16,511)	(5,899)	0
Net loss (income) attributable to noncontrolling interests									0	0	0
Net income attributable to Nelnet, Inc.									(16,511)	(5,899)	0
Total assets	214,336				103,104				214,336	103,104	68,760
Operating Segments [Member] | Asset Generation and Management [Member]
Segment Reporting Information [Line Items]
Total interest income									764,225	754,788	728,199
Interest expense									464,256	385,913	297,625
Net interest income									299,969	368,875	430,574
Less provision for loan losses									14,450	13,500	10,150
Net interest income (loss) after provision for loan losses									285,519	355,375	420,424
Other income:
Loan systems and servicing revenue									0	0	0
Intersegment servicing revenue									0	0	0
Tuition payment processing, school information, and campus commerce revenue									0	0	0
Communications revenue									0	0
Enrollment services revenue										0	0
Other income									13,424	15,709	15,939
Gain on sale of loans and debt repurchases, net									(1,567)	5,846	2,034
Derivative settlements, net									1,448	(21,034)	(23,238)
Derivative market value and foreign currency transaction adjustments, net									(19,357)	70,368	27,216
Total other income									(6,052)	70,889	21,951
Operating expenses:
Salaries and benefits									1,548	1,985	2,172
Depreciation and amortization									0	0	0
Loan servicing fees									22,734	25,750	30,213
Cost to provide communications services									0	0
Cost to provide enrollment services										0	0
Other expenses									3,900	6,005	5,083
Intersegment expenses, net									42,830	46,494	50,899
Total operating expenses									71,012	80,234	88,367
Income (loss) before income taxes									208,455	346,030	354,008
Income tax (expense) benefit									(79,213)	(131,492)	(134,522)
Net income (loss)									129,242	214,538	219,486
Net loss (income) attributable to noncontrolling interests									0	0	0
Net income attributable to Nelnet, Inc.									129,242	214,538	219,486
Total assets	22,910,974				26,378,467				22,910,974	26,378,467	29,634,280
Corporate and Other Activities [Member]
Segment Reporting Information [Line Items]
Total interest income									13,643	10,913	7,686
Interest expense									3,477	6,076	6,413
Net interest income									10,166	4,837	1,273
Less provision for loan losses									0	0	0
Net interest income (loss) after provision for loan losses									10,166	4,837	1,273
Other income:
Loan systems and servicing revenue									0	0	0
Intersegment servicing revenue									0	0	0
Tuition payment processing, school information, and campus commerce revenue									0	0	0
Communications revenue									0	0
Enrollment services revenue										4,326	51,073
Other income									39,402	38,221	32,248
Gain on sale of loans and debt repurchases, net									4,469	2,135	3,119
Derivative settlements, net									(781)	(915)	(1,012)
Derivative market value and foreign currency transaction adjustments, net									136	1,376	1,435
Total other income									43,226	45,143	86,863
Operating expenses:
Salaries and benefits									59,633	51,889	55,585
Depreciation and amortization									15,418	15,298	15,420
Loan servicing fees									0	0	0
Cost to provide communications services									0	0
Cost to provide enrollment services										3,623	41,733
Other expenses									51,381	45,843	44,971
Intersegment expenses, net									(44,208)	(32,889)	(38,868)
Total operating expenses									82,224	83,764	118,841
Income (loss) before income taxes									(28,832)	(33,784)	(30,705)
Income tax (expense) benefit									37,036	23,074	19,132
Net income (loss)									8,204	(10,710)	(11,573)
Net loss (income) attributable to noncontrolling interests									(1,295)	(750)	(305)
Net income attributable to Nelnet, Inc.									6,909	(11,460)	(11,878)
Total assets	877,859				682,459				877,859	682,459	624,953
Eliminations [Member]
Segment Reporting Information [Line Items]
Total interest income									(7,976)	(5,076)	(1,828)
Interest expense									(7,976)	(5,076)	(1,828)
Net interest income									0	0	0
Less provision for loan losses									0	0	0
Net interest income (loss) after provision for loan losses									0	0	0
Other income:
Loan systems and servicing revenue									0	0	0
Intersegment servicing revenue									(41,674)	(45,381)	(50,354)
Tuition payment processing, school information, and campus commerce revenue									0	0	0
Communications revenue									0	0
Enrollment services revenue										0	0
Other income									0	0	0
Gain on sale of loans and debt repurchases, net									0	0	0
Derivative settlements, net									0	0	0
Derivative market value and foreign currency transaction adjustments, net									0	0	0
Total other income									(41,674)	(45,381)	(50,354)
Operating expenses:
Salaries and benefits									0	0	0
Depreciation and amortization									0	0	0
Loan servicing fees									0	0	0
Cost to provide communications services									0	0
Cost to provide enrollment services										0	0
Other expenses									0	0	0
Intersegment expenses, net									(41,674)	(45,381)	(50,354)
Total operating expenses									(41,674)	(45,381)	(50,354)
Income (loss) before income taxes									0	0	0
Income tax (expense) benefit									0	0	0
Net income (loss)									0	0	0
Net loss (income) attributable to noncontrolling interests									0	0	0
Net income attributable to Nelnet, Inc.									0	0	0
Total assets	$ (411,415)				$ (256,687)				$ (411,415)	$ (256,687)	$ (218,923)