Acquisitions - Tables (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended
		Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Business Acquisition [Line Items]
Noncontrolling interest				$ (730)	$ (975)
Goodwill		$ 3,873,131	$ 3,848,798	3,873,131
U.S. Xpress
Business Acquisition [Line Items]
Fair value of the consideration transferred		632,109	632,109
Cash and cash equivalents		3,321	3,321	3,321
Receivables		217,004	216,659	217,004
Prepaid expenses		21,347	21,347	21,347
Other current assets		47,317	47,317	47,317
Property and equipment		433,210	433,210	433,210
Operating lease right-of-use assets		337,055	337,055	337,055
Identifiable intangible assets 1	[1]	348,000	348,000	348,000
Other noncurrent assets		28,457	28,457	28,457
Total assets		1,435,711	1,435,366	1,435,711
Accounts payable		(115,494)	(115,494)	(115,494)
Accrued payroll and payroll-related expenses		(27,485)	(27,485)	(27,485)
Accrued liabilities		(18,244)	(19,966)	(18,244)
Claims accruals – current and noncurrent portions		(180,251)	(180,251)	(180,251)
Operating lease liabilities – current and noncurrent portions		(376,763)	(376,763)	(376,763)
Long-term debt and finance leases – current and noncurrent portions		(337,949)	(337,949)	(337,949)
Deferred Tax Liabilities		(25,624)	(33,072)	(25,624)
Other long-term liabilities		(68,076)	(34,230)	(68,076)
Total liabilities		(1,149,886)	(1,125,210)	(1,149,886)
Noncontrolling interest		(391)	(391)
Total stockholders' equity		(391)	(391)	(391)
Goodwill		346,675	$ 322,344	346,675
Trade names		163,500		163,500
Total revenue					2,129,658
Net income attributable to Knight-Swift					$ 78,148
Earnings per share – diluted					$ 0.48
U.S. Xpress | Revision of Prior Period, Adjustment [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred		0
Cash and cash equivalents		0		0
Receivables		345		345
Prepaid expenses		0		0
Other current assets		0		0
Property and equipment		0		0
Operating lease right-of-use assets		0		0
Identifiable intangible assets 1		0		0
Other noncurrent assets		0		0
Total assets		345		345
Accounts payable		0		0
Accrued payroll and payroll-related expenses		0		0
Accrued liabilities		1,722		1,722
Claims accruals – current and noncurrent portions		0		0
Operating lease liabilities – current and noncurrent portions		0		0
Long-term debt and finance leases – current and noncurrent portions		0		0
Deferred Tax Liabilities		7,448		7,448
Other long-term liabilities		(33,846)		(33,846)
Total liabilities		(24,676)		(24,676)
Noncontrolling interest		0
Total stockholders' equity		0		0
Goodwill		24,331		24,331
U.S. Xpress | Customer relationships [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets		$ 184,500		$ 184,500

[1] Includes $184.5 million in customer relationships and $163.5 million in trade names.