Acquisitions - Tables (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		6 Months Ended
		Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Business Acquisition [Line Items]
Noncontrolling interest				$ (743)	$ (741)	$ (1,473)	$ (1,716)
Goodwill		$ 3,879,442	$ 3,848,798	3,879,442		3,879,442
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		3,321
Receivables		217,004	216,659	217,004		217,004
Prepaid expenses		21,347	21,347	21,347		21,347
Other current assets		47,317	47,317	47,317		47,317
Property and equipment		433,210	433,210	433,210		433,210
Operating lease right-of-use assets		337,055	337,055	337,055		337,055
Identifiable intangible assets 1	[1]	348,000	348,000	348,000		348,000
Other noncurrent assets		28,457	28,457	28,457		28,457
Total assets		1,435,711	1,435,366	1,435,711		1,435,711
Accounts payable		(117,094)	(115,494)	(117,094)		(117,094)
Accrued payroll and payroll-related expenses		(27,485)	(27,485)	(27,485)		(27,485)
Accrued liabilities		(20,775)	(19,966)	(20,775)		(20,775)
Claims accruals – current and noncurrent portions		(191,901)	(180,251)	(191,901)		(191,901)
Operating lease liabilities – current and noncurrent portions		(376,763)	(376,763)	(376,763)		(376,763)
Long-term debt and finance leases – current and noncurrent portions		(337,949)	(337,949)	(337,949)		(337,949)
Deferred Tax Liabilities		(23,130)	(33,072)	(23,130)		(23,130)
Other long-term liabilities		(61,102)	(34,230)	(61,102)		(61,102)
Total liabilities		(1,156,199)	(1,125,210)	(1,156,199)		(1,156,199)
Noncontrolling interest		(391)	(391)
Total stockholders' equity		(391)	(391)	(391)		(391)
Goodwill		352,988	$ 322,344	352,988		352,988
Trade names		163,500		163,500		163,500
Total revenue					2,015,537		4,145,195
Net income attributable to Knight-Swift					$ 34,790		$ 112,938
Earnings per share – diluted					$ 0.21		$ 0.70
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		0
Receivables		345		345		345
Prepaid expenses		0		0		0
Other current assets		0		0		0
Property and equipment		0		0		0
Operating lease right-of-use assets		0		0		0
Identifiable intangible assets 1		0		0		0
Other noncurrent assets		0		0		0
Total assets		345		345		345
Accounts payable		(1,600)		(1,600)		(1,600)
Accrued payroll and payroll-related expenses		0		0		0
Accrued liabilities		(809)		(809)		(809)
Claims accruals – current and noncurrent portions		(11,650)		(11,650)		(11,650)
Operating lease liabilities – current and noncurrent portions		0		0		0
Long-term debt and finance leases – current and noncurrent portions		0		0		0
Deferred Tax Liabilities		9,942		9,942		9,942
Other long-term liabilities		(26,872)		(26,872)		(26,872)
Total liabilities		(30,989)		(30,989)		(30,989)
Noncontrolling interest		0
Total stockholders' equity		0		0		0
Goodwill		30,644		30,644		30,644
U.S. Xpress | Customer relationships [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets		$ 184,500		$ 184,500		$ 184,500

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