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)							282
Common stock issued to employees	46	43			46			3
Common stock issued under ESPP (Shares)							21
Common stock issued under ESPP	1,040	1,040			1,040			0
Shares withheld – RSU settlement	(11,748)		(11,748)		(11,748)
Employee stock-based compensation expense	$ 7,927	7,927			7,927
Dividends declared per share: (in dollars per share)	$ 0.14
Cash dividends paid and dividends accrued	$ (22,730)		(22,730)		(22,730)
Net loss	104,284		104,284		104,284
Net loss attributable to noncontrolling interest	(571)					571
Net income	103,713
Other comprehensive loss	1,090			1,090	1,090
Investment in noncontrolling interest	975					975
Ending balance, shares at Mar. 31, 2023							161,009
Ending balance, value at Mar. 31, 2023	$ 7,035,594	4,401,276	2,623,373	(1,346)	7,024,913	10,681		1,610
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)							191
Common stock issued to employees	0	(2)			0			2
Common stock issued under ESPP (Shares)							17
Common stock issued under ESPP	953	952			953			1
Shares withheld – RSU settlement	(6,435)		(6,435)		(6,435)
Employee stock-based compensation expense	$ 3,981	3,981			3,981
Dividends declared per share: (in dollars per share)	$ 0.16
Cash dividends paid and dividends accrued	$ (26,019)		(26,019)		(26,019)
Net loss	(2,635)		(2,635)		(2,635)
Net loss attributable to noncontrolling interest	(358)					358
Net income	(2,993)
Other comprehensive loss	(38)			(38)	(38)
Investment in noncontrolling interest	730					730
Distribution to noncontrolling interest	$ (2,038)	(1,047)			(1,047)	(991)
Ending balance, shares at Mar. 31, 2024	161,593						161,593
Ending balance, value at Mar. 31, 2024	$ 7,072,222	$ 4,430,736	$ 2,624,666	$ (868)	$ 7,056,150	$ 16,072		$ 1,616