Consolidated Statements of Comprehensive Income - 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
Statement of Comprehensive Income [Abstract]
Net income	$ 45,714	$ 43,535	$ 24,651	$ 47,920	$ 98,931	$ 84,363	$ 26,178	$ 48,029	$ 161,821	$ 257,501	$ 268,264
Available-for-sale securities:
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