Condensed Consolidated Statement Of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent	Total Knight-Swift Equity [Member]	Noncontrolling Interest [Member]	Common Class A [Member]	Common Class A [Member] Common Stock
Beginning balance, shares at Dec. 31, 2022							160,706
Beginning balance, value at Dec. 31, 2022	$ 6,955,281	$ 4,392,266	$ 2,553,567	$ (2,436)	$ 6,945,004	$ 10,277		$ 1,607
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							565
Common stock issued to employees	163	158			163			5
Common stock issued to the Board (Shares)							18
Common stock issued to the Board	977	977			977			0
U.S. Xpress assumed equity awards	1,462	1,462			1,462
Common stock issued under ESPP (Shares)							58
Common stock issued under ESPP	3,060	3,059			3,060			1
Shares withheld – RSU settlement	(19,548)		(19,548)		(19,548)
Employee stock-based compensation expense	$ 21,059	21,059			21,059
Dividends declared per share: (in dollars per share)	$ 0.42
Cash dividends paid and dividends accrued	$ (68,255)		(68,255)		(68,255)
Net income (loss)	227,804		227,804		227,804
Net loss attributable to noncontrolling interest	(1,290)					(1,290)
Net income	226,514
Other comprehensive income	1,772			1,772	1,772
Investment in noncontrolling interest	7,555					7,555
Distribution to noncontrolling interest	(239)					(239)
Ending balance, shares at Sep. 30, 2023							161,347
Ending balance, value at Sep. 30, 2023	7,129,801	4,418,981	2,693,568	(664)	7,113,498	16,303		1,613
Beginning balance, shares at Jun. 30, 2023							161,276
Beginning balance, value at Jun. 30, 2023	7,081,043	4,412,069	2,657,415	(815)	7,070,282	10,761		1,613
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							53
Common stock issued to employees	0	0			0			0
U.S. Xpress assumed equity awards	1,462	1,462			1,462
Common stock issued under ESPP (Shares)							18
Common stock issued under ESPP	978	978			978			0
Shares withheld – RSU settlement	(1,277)		(1,277)		(1,277)
Employee stock-based compensation expense	$ 4,472	4,472			4,472
Dividends declared per share: (in dollars per share)	$ 0.14
Cash dividends paid and dividends accrued	$ (22,764)		(22,764)		(22,764)
Net income (loss)	60,194		60,194		60,194
Net loss attributable to noncontrolling interest	(297)					(297)
Net income	59,897
Other comprehensive income	151			151	151
Investment in noncontrolling interest	5,839					5,839
Ending balance, shares at Sep. 30, 2023							161,347
Ending balance, value at Sep. 30, 2023	$ 7,129,801	4,418,981	2,693,568	(664)	7,113,498	16,303		1,613
Beginning balance, shares at Dec. 31, 2023	161,385						161,385
Beginning balance, value at Dec. 31, 2023	$ 7,104,081	4,426,852	2,659,755	(830)	7,087,390	16,691		1,613
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							403
Common stock issued to employees	4	0			4			4
Common stock issued to the Board (Shares)							24
Common stock issued to the Board	1,206	1,206			1,206			0
U.S. Xpress assumed equity awards	0
Common stock issued under ESPP (Shares)							59
Common stock issued under ESPP	2,967	2,965			2,967			2
Shares withheld – RSU settlement	(11,839)		(11,839)		(11,839)
Employee stock-based compensation expense	$ 17,011	17,011			17,011
Dividends declared per share: (in dollars per share)	$ 0.48
Cash dividends paid and dividends accrued	$ (78,165)		(78,165)		(78,165)
Net income (loss)	48,129		48,129		48,129
Net loss attributable to noncontrolling interest	(1,170)					(1,170)
Net income	46,959
Other comprehensive income	998			998	998
Investment in noncontrolling interest	2,212					2,212
Distribution to noncontrolling interest	$ (19,218)	(9,005)			(9,005)	(10,213)
Ending balance, shares at Sep. 30, 2024	161,871						161,871
Ending balance, value at Sep. 30, 2024	$ 7,066,216	4,439,029	2,617,880	168	7,058,696	7,520		1,619
Beginning balance, shares at Jun. 30, 2024							161,836
Beginning balance, value at Jun. 30, 2024	7,070,353	4,439,489	2,613,684	(827)	7,053,964	16,389		1,618
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							10
Common stock issued to employees	0	0			0			0
Common stock issued under ESPP (Shares)							25
Common stock issued under ESPP	1,069	1,068			1,069			1
Shares withheld – RSU settlement	(188)		(188)		(188)
Employee stock-based compensation expense	$ 6,430	6,430			6,430
Dividends declared per share: (in dollars per share)	$ 0.16
Cash dividends paid and dividends accrued	$ (26,080)		(26,080)		(26,080)
Net income (loss)	30,464		30,464		30,464
Net loss attributable to noncontrolling interest	(405)					(405)
Net income	30,059
Other comprehensive income	995			995	995
Investment in noncontrolling interest	739					739
Distribution to noncontrolling interest	$ (17,161)	(7,958)			(7,958)	(9,203)
Ending balance, shares at Sep. 30, 2024	161,871						161,871
Ending balance, value at Sep. 30, 2024	$ 7,066,216	$ 4,439,029	$ 2,617,880	$ 168	$ 7,058,696	$ 7,520		$ 1,619