Condensed Parent Company Financial Statements - Condensed Parent Statement of Comprehensive 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
Net income	$ 45,714	$ 43,535	$ 24,651	$ 47,920	$ 98,931	$ 84,363	$ 26,178	$ 48,029	$ 161,821	$ 257,501	$ 268,264
Unrealized holding gains (losses) arising during period, net									2,349	5,789	(1,570)
Reclassification adjustment for gains recognized in net income, net of losses									(2,528)	(1,907)	(2,955)
Income tax effect									66	(1,436)	1,674
Total other comprehensive (loss) income									(113)	2,446	(2,851)
Comprehensive income									161,708	259,947	265,413
Comprehensive loss (income) attributable to noncontrolling interests									11,345	(750)	(285)
Comprehensive income attributable to Nelnet, Inc.									173,053	259,197	265,128
Parent Company [Member]
Net income									172,878	256,648	267,979
Unrealized holding gains (losses) arising during period, net									2,349	5,789	(1,570)
Reclassification adjustment for gains recognized in net income, net of losses									(2,528)	(1,907)	(2,955)
Income tax effect									66	(1,436)	1,674
Total other comprehensive (loss) income									(113)	2,446	(2,851)
Comprehensive income									172,765	259,094	265,128
Comprehensive loss (income) attributable to noncontrolling interests									288	103	0
Comprehensive income attributable to Nelnet, Inc.									$ 173,053	$ 259,197	$ 265,128