Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Cash Flows [Abstract]
Net income attributable to Nelnet, Inc.	$ 173,166	$ 256,751	$ 267,979
Net (loss) income attributable to noncontrolling interests	11,345	(750)	(285)
Net income	161,821	257,501	268,264
Adjustments to reconcile net income to net cash provided by operating activities, net of acquisitions:
Depreciation and amortization, including debt discounts and loan premiums and deferred origination costs	137,823	122,547	123,736
Loan discount accretion	(44,812)	(40,617)	(43,766)
Provision for loan losses	14,450	13,500	10,150
Derivative market value adjustment	(26,379)	(59,895)	15,150
Unrealized foreign currency transaction adjustment	45,600	(11,849)	(43,801)
(Payments) proceeds from termination of derivative instruments, net	(30,382)	3,999	65,527
Payments to enter into derivative instruments	(929)	0	(2,936)
Proceeds from clearinghouse to settle variation margin, net	48,985	0	0
Gain on sale of loans, net	0	0	(351)
Gain from debt repurchases, net	(2,902)	(7,981)	(4,802)
Gain from sales of available-for-sale securities, net of losses	(2,528)	(1,907)	(2,955)
Deferred income tax (benefit) expense	(1,544)	27,005	7,049
Non-cash compensation expense	4,416	4,348	5,347
Impairment expense	3,626	0	0
Other	3,948	4,215	755
Increase in loan accrued interest receivable	(39,203)	(7,439)	(3,819)
(Increase) decrease in accounts receivable	(12,046)	7,454	1,061
(Increase) decrease in other assets	(34,457)	(2,203)	375
Increase in accrued interest payable	4,362	14,170	5,117
(Decrease) increase in other liabilities	(2,341)	2,409	(8,736)
Net cash provided by operating activities	227,508	325,257	391,365
Cash flows from investing activities, net of acquisitions:
Purchases of loans	(325,476)	(349,144)	(2,189,450)
Net proceeds from loan repayments, claims, capitalized interest, and other	3,363,526	3,735,772	3,668,302
Proceeds from sale of loans	53,203	44,760	3,996
Purchases of available-for-sale securities	(128,523)	(94,673)	(100,476)
Proceeds from sales of available-for-sale securities	156,540	144,252	95,758
Purchases of investments and issuance of notes receivable	(29,339)	(22,361)	(93,948)
Proceeds from investments and notes receivable	11,545	15,898	29,799
Purchases of property and equipment	(156,005)	(67,602)	(16,761)
Decrease (increase) in restricted cash, net	320,108	(147,487)	67,108
Business and asset acquisitions, net of cash acquired	0	0	(46,966)
Proceeds from sale of business, net	4,511	0	0
Net cash provided by investing activities	3,270,090	3,259,415	1,417,362
Cash flows from financing activities, net of borrowings assumed:
Payments on bonds and notes payable	(5,403,224)	(4,134,890)	(4,368,180)
Proceeds from issuance of bonds and notes payable	1,984,558	650,909	2,614,595
Payments of debt issuance costs	(6,497)	(5,845)	(11,162)
Payment of contingent consideration	(850)	0	0
Dividends paid	(24,097)	(21,188)	(19,025)
Repurchases of common stock	(68,896)	(69,091)	(96,169)
Proceeds from issuance of common stock	678	889	801
Issuance of noncontrolling interests	19,473	1,241	3,693
Distribution to noncontrolling interests	(1,645)	(572)	(232)
Net cash used in financing activities	(3,500,500)	(3,578,547)	(1,875,679)
Net (decrease) increase in cash and cash equivalents	(2,902)	6,125	(66,952)
Cash and cash equivalents, beginning of year	69,654	63,529	130,481
Cash and cash equivalents, end of year	66,752	69,654	63,529
Cash disbursements made for:
Interest	390,278	301,118	228,248
Income taxes, net of refunds	96,721	115,415	147,235
Noncash investing and financing activities:
Loans and other assets acquired	0	0	2,025,453
Borrowings and other liabilities assumed in acquisition of loans	0	0	1,885,453
Issuance of noncontrolling interest	$ 0	$ 20	$ 3,750