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)							512
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
Common stock issued under ESPP (Shares)							40
Common stock issued under ESPP	2,082	2,081			2,082			1
Shares withheld – RSU settlement	(18,271)		(18,271)		(18,271)
Employee stock-based compensation expense	$ 16,587	16,587			16,587
Dividends declared per share: (in dollars per share)	$ 0.28
Cash dividends paid and dividends accrued	$ (45,491)		(45,491)		(45,491)
Net income (loss)	167,610		167,610		167,610
Net loss attributable to noncontrolling interest	(993)					(993)
Net income	166,617
Other comprehensive loss	1,621			1,621	1,621
Investment in noncontrolling interest	1,716
Distribution to noncontrolling interest	(239)					(239)
Ending balance, shares at Jun. 30, 2023							161,276
Ending balance, value at Jun. 30, 2023	7,081,043	4,412,069	2,657,415	(815)	7,070,282	10,761		1,613
Beginning balance, shares at Mar. 31, 2023							161,009
Beginning balance, value at Mar. 31, 2023	7,035,594	4,401,276	2,623,373	(1,346)	7,024,913	10,681		1,610
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							230
Common stock issued to employees	117	115			117			2
Common stock issued to the Board (Shares)							18
Common stock issued to the Board	977	977			977			0
Common stock issued under ESPP (Shares)							19
Common stock issued under ESPP	1,042	1,041			1,042			1
Shares withheld – RSU settlement	(6,523)		(6,523)		(6,523)
Employee stock-based compensation expense	$ 8,660	8,660			8,660
Dividends declared per share: (in dollars per share)	$ 0.14
Cash dividends paid and dividends accrued	$ (22,761)		(22,761)		(22,761)
Net income (loss)	63,326		63,326		63,326
Net loss attributable to noncontrolling interest	(422)					(422)
Net income	62,904
Other comprehensive loss	531			531	531
Investment in noncontrolling interest	741
Distribution to noncontrolling interest	(239)					(239)
Ending balance, shares at Jun. 30, 2023							161,276
Ending balance, value at Jun. 30, 2023	$ 7,081,043	4,412,069	2,657,415	(815)	7,070,282	10,761		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)							393
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
Common stock issued under ESPP (Shares)							34
Common stock issued under ESPP	1,898	1,897			1,898			1
Shares withheld – RSU settlement	(11,651)		(11,651)		(11,651)
Employee stock-based compensation expense	$ 10,581	10,581			10,581
Dividends declared per share: (in dollars per share)	$ 0.32
Cash dividends paid and dividends accrued	$ (52,085)		(52,085)		(52,085)
Net income (loss)	17,665		17,665		17,665
Net loss attributable to noncontrolling interest	(765)					(765)
Net income	16,900
Other comprehensive loss	3			3	3
Investment in noncontrolling interest	1,473					1,473
Distribution to noncontrolling interest	$ (2,057)	(1,047)			(1,047)	(1,010)
Ending balance, shares at Jun. 30, 2024	161,836						161,836
Ending balance, value at Jun. 30, 2024	$ 7,070,353	4,439,489	2,613,684	(827)	7,053,964	16,389		1,618
Beginning balance, shares at Mar. 31, 2024							161,593
Beginning balance, value at Mar. 31, 2024	7,072,222	4,430,736	2,624,666	(868)	7,056,150	16,072		1,616
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							202
Common stock issued to employees	2	0			2			2
Common stock issued to the Board (Shares)							24
Common stock issued to the Board	1,208	1,208			1,208			0
Common stock issued under ESPP (Shares)							17
Common stock issued under ESPP	945	945			945			0
Shares withheld – RSU settlement	(5,216)		(5,216)		(5,216)
Employee stock-based compensation expense	$ 6,600	6,600			6,600
Dividends declared per share: (in dollars per share)	$ 0.16
Cash dividends paid and dividends accrued	$ (26,066)		(26,066)		(26,066)
Net income (loss)	20,300		20,300		20,300
Net loss attributable to noncontrolling interest	(407)					(407)
Net income	19,893
Other comprehensive loss	41			41	41
Investment in noncontrolling interest	743					743
Distribution to noncontrolling interest	$ (19)					(19)
Ending balance, shares at Jun. 30, 2024	161,836						161,836
Ending balance, value at Jun. 30, 2024	$ 7,070,353	$ 4,439,489	$ 2,613,684	$ (827)	$ 7,053,964	$ 16,389		$ 1,618