Condensed Parent Company Financial Statements - Condensed Parent Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment interest									$ 12,695	$ 9,466	$ 7,851
Interest on bonds and notes payable									465,188	388,183	302,210
Net interest income (expense)	$ 73,235	$ 75,237	$ 79,842	$ 76,925	$ 78,960	$ 99,795	$ 92,200	$ 101,609	305,238	372,563	431,899
Other income (expense):
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 from debt repurchases, net	(2,635)	116	442	4,980	5,720	2,160	0	101	2,902	7,981	5,153
Derivative market value and foreign currency transaction adjustments and derivative settlements, net	7,014	7,173	(27,910)	(4,830)	83,187	36,001	(40,702)	(28,691)	(18,554)	49,795	4,401
Total other income									431,625	481,266	468,112
Operating expenses									495,729	441,515	469,217
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	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
Parent Company [Member]
Investment interest									13,060	9,794	5,776
Interest on bonds and notes payable									3,315	6,049	6,242
Net interest income (expense)									9,745	3,745	(466)
Other income (expense):
Other income									3,483	7,037	4,012
Gain from debt repurchases, net									2,964	8,083	4,904
Equity in subsidiaries income									170,897	239,405	276,825
Derivative market value and foreign currency transaction adjustments and derivative settlements, net									(603)	45,203	8,416
Total other income									176,741	299,728	294,157
Operating expenses									6,117	8,183	5,057
Income before income taxes									180,369	295,290	288,634
Income tax (expense) benefit									(7,491)	(38,642)	(20,655)
Net income									172,878	256,648	267,979
Net (loss) income attributable to noncontrolling interests									288	103	0
Net income attributable to Nelnet, Inc.									$ 173,166	$ 256,751	$ 267,979