Knight-Swift Transportation (KNX) 10-Q 3 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 27, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-35007
Entity Registrant Name	Knight-Swift Transportation Holdings Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-5589597
Entity Address, Address Line One	2002 West Wahalla Lane
Entity Address, City or Town	Phoenix
Entity Address, State or Province	AZ
Entity Address, Postal Zip Code	85027
City Area Code	602
Local Phone Number	269-2000
Title of 12(b) Security	Common Stock $0.01 Par Value
Trading Symbol	KNX
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		165,957,149
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001492691
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) shares in Thousands, $ in Thousands		Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents		$ 269,694	$ 156,699
Cash and cash equivalents – restricted	[1]	68,019	39,328
Restricted investments, held-to-maturity, amortized cost	[2]	7,140	9,001
Trade receivables, net of allowance for doubtful accounts of $21,811 and $22,093, respectively		830,402	578,479
Contract balance – revenue in transit		22,950	14,560
Prepaid expenses		76,697	71,649
Assets held for sale		20,330	29,756
Income tax receivable		46,899	2,903
Other current assets		62,334	20,988
Total current assets		1,404,465	923,363
Gross property and equipment		4,933,669	4,223,348
Less: accumulated depreciation and amortization		(1,477,334)	(1,230,696)
Property and equipment, net		3,456,335	2,992,652
Operating lease right-of-use-assets		102,230	113,296
Goodwill		3,461,898	2,922,964
Intangible assets, net		1,793,924	1,389,245
Other long-term assets		136,130	126,482
Total assets		10,354,982	8,468,002
Current liabilities:
Accounts payable		177,634	101,001
Accrued payroll and purchased transportation		227,016	160,888
Accrued liabilities		134,002	88,894
Claims accruals – current portion		200,159	174,928
Finance lease liabilities and long-term debt – current portion		78,266	52,583
Operating lease liabilities – current portion		35,464	47,496
Accounts receivable securitization – current portion		0	213,918
Total current liabilities		852,541	839,708
Revolving line of credit		300,000	210,000
Long-term debt – less current portion		1,238,022	298,907
Finance lease liabilities – less current portion		208,556	138,243
Operating lease liabilities – less current portion		69,401	69,852
Accounts receivable securitization – less current portion		278,428	0
Claims accruals – less current portion		200,493	174,814
Deferred tax liabilities		856,926	815,941
Other long-term liabilities		45,175	48,497
Total liabilities		4,049,542	2,595,962
Commitments and contingencies (Notes 3, 10, 11, and 12)
Stockholders’ equity:
Preferred stock, par value $0.01 per share; 10,000 shares authorized; none issued		$ 0	$ 0
Parenthetical - Preferred stock, par value (in dollars per share)		$ 0.01	$ 0.01
Parenthetical - Preferred stock, shares authorized (in shares)		10,000	10,000
Parenthetical - Preferred stock, shares issued (in shares)		0	0
Common stock, par value $0.01 per share; 500,000 shares authorized; 166,003 and 166,553 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively.		$ 1,660	$ 1,665
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01
Common stock, shares authorized (in shares)		500,000	500,000
Common stock, shares issued (in shares)		166,003	166,553
Common stock, shares outstanding (in shares)		166,003	166,553
Additional paid-in capital		$ 4,344,894	$ 4,301,424
Accumulated other comprehensive loss		(878)	0
Retained earnings		1,946,984	1,566,759
Total Knight-Swift stockholders' equity		6,292,660	5,869,848
Noncontrolling interest		12,780	2,192
Total stockholders’ equity		6,305,440	5,872,040
Total liabilities and stockholders’ equity		$ 10,354,982	$ 8,468,002
Common Class A [Member]
Stockholders’ equity:
Common stock, shares outstanding (in shares)		166,003	166,553
[1]	Reflects cash and cash equivalents that are primarily restricted for claims payments.
[2]	Refer to Note 4 for the differences between the carrying amounts and estimated fair values of the Company's restricted investments, held-to-maturity.

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Total revenue	$ 1,642,445	$ 1,210,406	$ 4,181,160	$ 3,395,902
Operating expenses:
Salaries, wages, and benefits	500,673	376,923	1,248,656	1,097,067
Fuel	146,422	104,703	390,713	312,939
Operations and maintenance	86,951	69,964	226,334	204,435
Insurance and claims	73,757	45,186	188,176	144,768
Operating taxes and licenses	27,475	21,475	71,240	64,527
Communications	6,612	5,069	16,284	14,845
Depreciation and amortization of property and equipment	138,570	115,664	382,091	340,486
Amortization of intangibles	15,719	11,473	39,452	34,421
Rental expense	12,002	19,700	42,265	67,447
Purchased transportation	352,061	245,102	914,448	670,485
Impairments	0	0	0	1,255
Miscellaneous operating expenses	12,116	29,686	38,040	73,480
Total operating expenses	1,372,358	1,044,945	3,557,699	3,026,155
Operating income	270,087	165,461	623,461	369,747
Other (expenses) income:
Interest income	245	326	809	1,595
Interest expense	(7,179)	(3,232)	(13,972)	(13,360)
Other income, net	4,072	7,484	37,017	9,476
Total other (expenses) income, net	(2,862)	4,578	23,854	(2,289)
Income before income taxes	267,225	170,039	647,315	367,458
Income tax expense	61,059	47,835	158,171	99,204
Net income	206,166	122,204	489,144	268,254
Net income attributable to noncontrolling interest	12	(146)	(372)	(581)
Net income attributable to Knight-Swift	206,178	122,058	488,772	267,673
Other comprehensive loss	(878)	0	(878)	0
Comprehensive income	$ 205,300	$ 122,058	$ 487,894	$ 267,673
Earnings per share:
Basic (in dollars per share)	$ 1.24	$ 0.72	$ 2.95	$ 1.57
Diluted (in dollars per share)	1.23	0.71	2.93	1.57
Dividends declared per share: (in dollars per share)	$ 0.10	$ 0.08	$ 0.28	$ 0.24
Weighted average shares outstanding:
Basic (in shares)	165,966	170,205	165,823	170,257
Diluted (in shares)	167,106	171,028	166,936	171,035
Revenue, excluding truckload fuel surcharge
Total revenue	$ 1,510,572	$ 1,137,313	$ 3,856,549	$ 3,162,005
Truckload fuel surcharge
Total revenue	$ 131,873	$ 73,093	$ 324,611	$ 233,897

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Statement of Cash Flows [Abstract]
Net income	$ 489,144	$ 268,254
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of property, equipment, and intangibles	421,543	374,907
Gain on sale of property and equipment	(47,700)	(6,468)
Impairments	0	1,255
Deferred income taxes	40,987	32,565
Non-cash lease expense	35,939	64,301
Non-cash adjustment to fair value of convertible note	(12,631)	0
Other adjustments to reconcile net income to net cash provided by operating activities	17,372	24,513
Increase (decrease) in cash resulting from changes in:
Trade receivables	(152,482)	(58,246)
Income tax receivable	(43,462)	8,668
Accounts payable	34,255	1,946
Accrued liabilities and claims accrual	57,157	(12,926)
Operating lease liabilities	(37,357)	(66,333)
Other assets and liabilities	14,759	22,583
Net cash provided by operating activities	817,524	655,019
Cash flows from investing activities:
Proceeds from maturities of held-to-maturity investments	8,380	9,400
Purchases of held-to-maturity investments	(6,683)	(12,644)
Proceeds from sale of property and equipment, including assets held for sale	192,454	102,550
Purchases of property and equipment	(388,518)	(378,694)
Expenditures on assets held for sale	(1,367)	(483)
Net cash, restricted cash, and equivalents invested in acquisitions	(1,342,042)	(46,811)
Payments to Acquire Debt Securities, Available-for-sale	(25,000)	0
Other cash flows from investing activities	14,019	(8,920)
Net cash used in investing activities	(1,548,757)	(335,602)
Cash flows from financing activities:
Repayment of finance leases and long-term debt	(374,539)	(61,321)
Proceeds from long-term debt	1,200,000	0
Borrowings (repayments) on revolving lines of credit, net	90,000	(109,000)
Borrowings under accounts receivable securitization	80,000	49,000
Repayment of accounts receivable securitization	(15,000)	(52,000)
Proceeds from common stock issued	7,624	11,632
Repurchases of the Company's common stock	(53,661)	(34,630)
Dividends paid	(46,935)	(41,297)
Other cash flows from financing activities	(14,180)	(5,522)
Net cash provided by (used in) financing activities	873,309	(243,138)
Net increase in cash, restricted cash, and equivalents	142,076	76,279
Cash, restricted cash, and equivalents at beginning of period	197,277	202,228
Cash, restricted cash, and equivalents at end of period	339,353	278,507
Cash paid during the period for:
Interest	11,683	12,921
Income taxes	160,281	35,233
Other Significant Noncash Transactions [Line Items]
Equipment acquired included in accounts payable	9,278	45,430
Contingent consideration associated with acquisition	5,000	18,245
Value of common stock issued for acquisition	10,000	0
Right-of-use assets obtained in exchange for operating lease liabilities	20,261	1,871
Property and equipment obtained in exchange for finance lease liabilities reclassified from operating lease liabilities	114,803	68,590
Financing provided to independent contractors for equipment sold [Member]
Other Significant Noncash Transactions [Line Items]
Other non-cash investing and financing activities	2,548	4,359
Transfers from property and equipment to assets held for sale [Member]
Other Significant Noncash Transactions [Line Items]
Other non-cash investing and financing activities	80,881	59,543
Noncontrolling Interest Associated With Acquisition
Other Significant Noncash Transactions [Line Items]
Other non-cash investing and financing activities	10,281	0
Property and equipment obtained in exchange for finance lease liabilities from operating lease liabilities
Other Significant Noncash Transactions [Line Items]
Property and equipment obtained in exchange for finance lease liabilities reclassified from operating lease liabilities	42,298	67,430
2021 Acquisitions
Other Significant Noncash Transactions [Line Items]
Right-of-use assets obtained in exchange for operating lease liabilities	$ 4,613
Warehousing Co [Member]
Other Significant Noncash Transactions [Line Items]
Right-of-use assets obtained in exchange for operating lease liabilities		$ 12,356

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) Reconciliation of Cash, Restricted Cash, and Cash Equivalents - USD ($) $ in Thousands		Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Statement of Cash Flows [Abstract]
Cash and cash equivalents		$ 269,694	$ 156,699	$ 240,236	$ 159,722
Cash and cash equivalents – restricted	[1]	68,019	39,328	36,689	41,331
Other long-term assets	[1]	1,640	1,250	1,582	1,175
Cash, restricted cash, and equivalents		$ 339,353	$ 197,277	$ 278,507	$ 202,228
[1]	Reflects cash and cash equivalents that are primarily restricted for claims payments.

Condensed Consolidated Statem_4

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, 2019							170,688
Beginning balance, value at Dec. 31, 2019	$ 5,668,303	$ 4,269,043	$ 1,395,465	$ 0	$ 5,666,215	$ 2,088		$ 1,707
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							609
Common stock issued to employees	9,480	9,474			9,480			6
Common stock issued to the Board (Shares)							13
Common stock issued to the Board	515	515			515			0
Value of common stock issued for acquisition	0
Common stock issued under ESPP (Shares)							47
Common stock issued under ESPP	1,637	1,637			1,637			0
Company shares repurchased (Shares)							(1,139)
Company shares repurchased	(34,630)		(34,619)		(34,630)			(11)
Shares withheld – RSU settlement	(4,508)		(4,508)		(4,508)
Employee stock-based compensation expense	$ 13,835	13,835			13,835
Dividends declared per share: (in dollars per share)	$ 0.24
Cash dividends paid and dividends accrued	$ (41,197)		(41,197)		(41,197)
Net income attributable to Knight-Swift	267,673		267,673		267,673
Distribution to noncontrolling interest	(441)					(441)
Net income attributable to noncontrolling interest	581					581
Ending balance, shares at Sep. 30, 2020							170,218
Ending balance, value at Sep. 30, 2020	5,881,248	4,294,504	1,582,814	0	5,879,020	2,228		1,702
Beginning balance, shares at Jun. 30, 2020							170,162
Beginning balance, value at Jun. 30, 2020	5,765,589	4,287,293	1,474,466	0	5,763,460	2,129		1,701
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							42
Common stock issued to employees	1,166	1,165			1,166			1
Common stock issued under ESPP (Shares)							14
Common stock issued under ESPP	574	574			574			0
Shares withheld – RSU settlement	(8)		(8)		(8)
Employee stock-based compensation expense	$ 5,472	5,472			5,472
Dividends declared per share: (in dollars per share)	$ 0.08
Cash dividends paid and dividends accrued	$ (13,702)		(13,702)		(13,702)
Net income attributable to Knight-Swift	122,058		122,058		122,058
Distribution to noncontrolling interest	(47)					(47)
Net income attributable to noncontrolling interest	146					146
Ending balance, shares at Sep. 30, 2020							170,218
Ending balance, value at Sep. 30, 2020	$ 5,881,248	4,294,504	1,582,814	0	5,879,020	2,228		1,702
Beginning balance, shares at Dec. 31, 2020	166,553						166,553
Beginning balance, value at Dec. 31, 2020	$ 5,872,040	4,301,424	1,566,759	0	5,869,848	2,192		1,665
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							475
Common stock issued to employees	5,026	5,020			5,026			6
Common stock issued to the Board (Shares)							12
Common stock issued to the Board	575	575			575			0
Common stock issued for acquisition (Shares)							219
Value of common stock issued for acquisition	10,000	9,998			10,000			2
Common stock issued under ESPP (Shares)							47
Common stock issued under ESPP	2,023	2,023			2,023			0
Company shares repurchased (Shares)							(1,303)
Company shares repurchased	(53,661)		(53,648)		(53,661)			(13)
Shares withheld – RSU settlement	(8,079)		(8,079)		(8,079)
Employee stock-based compensation expense	$ 25,854	25,854			25,854
Dividends declared per share: (in dollars per share)	$ 0.28
Cash dividends paid and dividends accrued	$ (46,820)		(46,820)		(46,820)
Net income attributable to Knight-Swift	488,772		488,772		488,772
Other comprehensive loss	(878)			(878)	(878)
Investment in noncontrolling interest	10,281					10,281
Distribution to noncontrolling interest	(65)					(65)
Net income attributable to noncontrolling interest	$ 372					372
Ending balance, shares at Sep. 30, 2021	166,003						166,003
Ending balance, value at Sep. 30, 2021	$ 6,305,440	4,344,894	1,946,984	(878)	6,292,660	12,780		1,660
Beginning balance, shares at Jun. 30, 2021							165,711
Beginning balance, value at Jun. 30, 2021	6,098,053	4,325,915	1,757,689	0	6,085,261	12,792		1,657
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued to employees (Shares)							57
Common stock issued to employees	1,630	1,629			1,630			1
Common stock issued for acquisition (Shares)							219
Value of common stock issued for acquisition	10,000	9,998			10,000			2
Common stock issued under ESPP (Shares)							16
Common stock issued under ESPP	692	692			692			0
Shares withheld – RSU settlement	(132)		(132)		(132)
Employee stock-based compensation expense	$ 6,660	6,660			6,660
Dividends declared per share: (in dollars per share)	$ 0.10
Cash dividends paid and dividends accrued	$ (16,751)		(16,751)		(16,751)
Net income attributable to Knight-Swift	206,178		206,178		206,178
Other comprehensive loss	(878)			(878)	(878)
Net income attributable to noncontrolling interest	$ (12)					(12)
Ending balance, shares at Sep. 30, 2021	166,003						166,003
Ending balance, value at Sep. 30, 2021	$ 6,305,440	$ 4,344,894	$ 1,946,984	$ (878)	$ 6,292,660	$ 12,780		$ 1,660

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited)(Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Receivables [Abstract]
Parenthetical - allowance for doubtful accounts	$ 21,811	$ 22,093

Introduction and Basis of Prese

Introduction and Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Introduction and Basis of Presentation	Introduction and Basis of Presentation Certain acronyms and terms used throughout this Quarterly Report are specific to the Company, commonly used in the trucking industry, or are otherwise frequently used throughout this document. Definitions for these acronyms and terms are provided in the "Glossary of Terms," available in the front of this document. Description of Business Knight-Swift is a transportation solutions provider, headquartered in Phoenix, Arizona. During the year-to-date period ended September 30, 2021, the Company operated an average of 18,041 tractors (comprised of 16,166 company tractors and 1,875 independent contractor tractors) and 60,396 trailers within the Truckload segment. Additionally, the Company operated an average of 605 tractors and 10,843 containers in the Intermodal segment. As of September 30, 2021 , the Company's four reportable segments were Truckload, Logistics, Intermodal, and LTL. Basis of Presentation The condensed consolidated financial statements and footnotes included in this Quarterly Report include the accounts of Knight-Swift Transportation Holdings Inc. and its subsidiaries and should be read in conjunction with the consolidated financial statements and footnotes included in Knight-Swift's 2020 Annual Report. In management's opinion, these condensed consolidated financial statements were prepared in accordance with GAAP and include all adjustments necessary (consisting of normal recurring adjustments) for the fair statement of the periods presented. With respect to transactional/durational data, references to years pertain to calendar years. Similarly, references to quarters pertain to calendar quarters. Note regarding comparability — The reported results do not include ACT's operating results prior to its acquisition by the Company on July 5, 2021 in accordance with the accounting treatment applicable to the transaction. Accordingly, comparisons between the Company's third quarter 2021 results and prior periods may not be meaningful. Change in Accounting Estimate In September 2021, the Company increased the useful life for a certain group of its trailers, given recent trends in the used trailer market. Management prospectively accounted for this as a change in accounting estimate. This increased "Depreciation and amortization of property and equipment" in the condensed consolidated statements of comprehensive income by approximately $0.6 million for the quarter and year-to-date periods ended September 30, 2021, which immaterially affected basic and diluted earnings per share. Seasonality In the truckload transportation industry, results of operations generally follow a seasonal pattern. Freight volumes in the first quarter are typically lower due to less consumer demand, customers reducing shipments following the holiday season, and inclement weather. At the same time, operating expenses generally increase, and tractor productivity of the Company's Truckload fleet, independent contractors, and third-party carriers decreases during the winter months due to decreased fuel efficiency, increased cold weather-related equipment maintenance and repairs, and increased insurance claims and costs attributed to higher accident frequency from harsh weather. These factors typically lead to lower operating profitability, as compared to other parts of the year. Additionally, beginning in the latter half of the third quarter and continuing into the fourth quarter, the Company typically experiences surges pertaining to holiday shopping trends toward delivery of gifts purchased over the Internet, as well as the length of the holiday season (consumer shopping days between Thanksgiving and Christmas). However, as the Company continues to diversify its business through expansion into the LTL industry, warehousing, and other activities, seasonal volatility is becoming more tempered. Additionally, macroeconomic trends and cyclical changes in the trucking industry, including imbalances in supply and demand, can override the seasonality faced in the industry. Impact of COVID-19 The Company continues to operate its business through the COVID-19 pandemic, including its variants, and has taken additional precautions to ensure the safety of its employees, customers, vendors, and the communities in which it operates. There are various uncertainties that have arisen from the COVID-19 pandemic. While management is continuing to monitor the impact of the pandemic on Knight-Swift, including its employees, customers, independent contractors, stockholders, and other business partners and stakeholders, it is difficult to predict the impact that the pandemic will have on future results of its operations, financial position, and liquidity. This has caused some uncertainties around various accounting estimates. Due to these uncertainties, the Company's accounting estimates may change, as management's assessment of the impacts of the COVID-19 pandemic continues to evolve.

Recently Issued Accounting Pron

Recently Issued Accounting Pronouncements	9 Months Ended
	Sep. 30, 2021
Accounting Changes and Error Corrections [Abstract]
Recently Issued Accounting Pronouncements	Recently Issued Accounting PronouncementsThere have been no ASUs issued since the filing date of the 2020 Annual Report that may have a material impact on the Company.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Acquisition	Acquisitions ACT On July 5, 2021, the Company acquired 100% of Dothan, Alabama-based ACT. ACT is a leading LTL carrier that also offers dedicated contract carriage and ancillary services. The total purchase price consideration of $1.31 billion included $1.30 billion in cash and $10.0 million in Knight-Swift shares issued to sellers at closing. Additionally, the Company assumed $36.5 million in debt, net of cash. Cash was funded from the July 2021 Term Loan, as well as existing Knight-Swift liquidity. ACT was an S corporation for tax purposes, and the transaction included an election under Internal Revenue Code Section 338(h)(10). Accordingly, the book and tax basis of the acquired assets and liabilities are the same as of the purchase date. The SPA contains customary representations, warranties, and covenants. The Company's condensed consolidated financial statements for the quarter and year-to-date periods ended September 30, 2021 include ACT's operating results beginning July 5, 2021 (closing of the acquisition) through September 30, 2021. During the quarter and year-to-date periods ended September 30, 2021, the Company's consolidated operating results included ACT's total revenue of $191.9 million and net income of $13.4 million. ACT's net income, during the quarter and year-to-date periods ended September 30, 2021, included $3.5 million related to the amortization of intangible assets acquired in the ACT Acquisition. The goodwill recognized represents expected synergies from combining the operations of ACT with the Company, including enhanced service offerings, as well as other intangible assets that did not meet the criteria for separate recognition. The goodwill is expected to be deductible for tax purposes. Pro Forma Information — The following unaudited pro forma information combines the historical operations of the Company and ACT giving effect to the ACT Acquisition, and related transactions as if consummated on January 1, 2020, the beginning of the comparative period presented. Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 (in thousands, except per share data) (in thousands, except per share data) Total revenue $ 1,642,445 $ 1,388,490 $ 4,570,470 $ 3,911,986 Net income attributable to Knight-Swift 202,883 129,295 507,168 284,095 Earnings per share – diluted 1.21 0.76 3.04 1.66 The unaudited pro forma condensed combined financial information has been presented for comparative purposes only and includes certain adjustments such as recognition of assets acquired at estimated fair values and related depreciation and amortization, elimination of transaction costs incurred by Knight-Swift and ACT during the periods presented that were directly related to the ACT Acquisition, and related income tax effects of these items. As a result of the ACT Acquisition, the Company incurred certain acquisition-related expenses totaling $2.4 million and $2.7 million during the quarter and year-to-date periods ended September 30, 2021, respectively. These expenses were eliminated in the presentation of the unaudited pro forma "Net income attributable to Knight-Swift" presented above. The unaudited pro forma condensed combined financial information does not purport to represent the actual results of operations that Knight-Swift and ACT would have achieved had the companies been combined during the periods presented in the unaudited pro forma condensed combined financial statements and is not intended to project the future results of operations that the combined company may achieve after the identified transactions. The unaudited pro forma condensed combined financial information does not reflect any cost savings that may be realized as a result of the ACT Acquisition and also does not reflect any restructuring or integration-related costs to achieve those potential cost savings. UTXL On June 1, 2021, pursuant to an SPA the Company, through a wholly owned subsidiary, acquired 100.0% of the equity interests of UTXL, a premier third-party logistics company which specializes in over-the-road full truckload and multi-stop loads. The total purchase price consideration of $37.2 million, including cash on hand and net working capital adjustments, consisted of $32.2 million in cash to the sellers at closing, which was funded through cash-on-hand and borrowing on the 2017 Revolver on the transaction date. At closing $2.25 million of the cash consideration was placed in escrow to secure certain of the sellers' indemnification obligations and remains subject to further adjustments. The purchase price also included contingent consideration consisting of two additional annual payments of up to $2.5 million each (or $5.0 million in total), representing the maximum possible annual deferred payments to the sellers based on operating ratio and revenue growth targets for each of the twelve-month periods ending May 31, 2022 and May 31, 2023. As of September 30, 2021, $2.5 million is included in "Accrued liabilities" and $2.5 million is included in "Other long-term liabilities" in the Company's condensed consolidated balance sheets, depending on the expected payment dates. For income tax purposes, the sale of UTXL's equity interests to the Company is intended to be treated as a sale and purchase of assets. Accordingly, the book and tax basis of the acquired assets and liabilities are the same as of the purchase date. The SPA contains customary representations, warranties, covenants, and indemnification provisions. The goodwill recognized represents expected synergies from combining the operations of UTXL with the Company, including enhanced service offerings, as well as other intangible assets that did not meet the criteria for separate recognition. The goodwill is expected to be deductible for tax purposes. Eleos On February 1, 2021, pursuant to a membership interest purchase agreement ("MIPA"), the Company, through a wholly owned subsidiary, acquired 79.44% of the issued and outstanding membership interests of Eleos Technologies, LLC ("Eleos"), a Greenville, South Carolina based software provider, specializing in mobile driving platforms, which complement the Company's suite of services. The total purchase price consideration, including cash on hand and net working capital adjustments, consisted of $41.5 million in cash to the sellers at closing, which was funded through cash-on-hand and borrowing on the Revolver on the transaction date. At closing, $4.1 million of the cash consideration was placed in escrow to secure certain of the sellers' indemnification obligations and other items. The MIPA included that both the buyer and sellers would file an election under the Internal Revenue Code Section 754 to adjust the tax basis of the Company's assets and liabilities, with respect to the buyer's purchase of the equity. The MIPA contains customary representations, warranties, covenants, and indemnification provisions for transactions of this nature. The goodwill recognized represents expected synergies from combining the operations of Eleos with the Company, including enhanced service offerings, as well as other intangible assets that did not meet the criteria for separate recognition. The goodwill is expected to be deductible for tax purposes. Purchase Price Allocations The purchase price allocations for the below acquisitions are preliminary and have been allocated based on estimated fair values of the assets acquired and liabilities assumed at the acquisition date, and among other things may be pending the completion of the valuation of acquired tangible assets, an independent valuation of certain acquired intangible assets, assessment of lease agreements, assessment of certain liabilities, the calculation of deferred taxes based upon the underlying tax basis of assets acquired and liabilities assumed, and assessment of other tax related items as applicable. As the Company obtains more information, the preliminary purchase price allocations disclosed below are subject to change. Any future adjustments to the preliminary purchase price allocations, including changes within identifiable intangible assets or estimation uncertainty impacted by market conditions, may impact future net earnings. The purchase price allocation adjustments can be made through the end of the measurement periods, which is not to exceed one year from the respective acquisition dates. ACT UTXL Eleos July 5, 2021 Opening Balance Sheet as Reported at September 30, 2021 June 1, 2021 Opening Balance Sheet as Reported at September 30, 2021 February 1, 2021 Opening Balance Sheet as Reported at September 30, 2021 Fair value of the consideration transferred $ 1,306,214 $ 37,230 $ 41,518 Cash and cash equivalents 17,477 8,206 2,237 Trade receivables 104,220 9,451 545 Prepaid expenses 15,803 — 47 Other current assets 3,537 — — Property and equipment 427,722 54 — Operating lease right-of-use assets 4,053 — 560 Identifiable intangible assets 1 406,160 22,121 15,850 Other noncurrent assets 1,739 — — Total assets 980,711 39,832 19,239 Accounts payable (19,386) (14,183) (156) Accrued payroll and payroll-related expenses (33,411) (247) (605) Accrued liabilities (9,302) (69) (1,391) Claims accruals – current and noncurrent portions (40,958) (418) — Operating lease liabilities – current and noncurrent portions (4,052) — (560) Long-term debt – current and noncurrent portions (54,024) — — Other long-term liabilities (4,243) — (475) Total liabilities (165,376) (14,917) (3,187) Noncontrolling interest — — (10,281) Total stockholders' equity — — (10,281) Goodwill $ 490,879 $ 12,315 $ 35,747 1 Includes $278.8 million in customer relationships, $1.2 million in noncompete agreements, $10.0 million in internally developed software, and $154.1 million in trade names. Warehousing Co. Information about the accounting treatment for the acquisition of Warehousing Co., including the details of the transaction, determination of the total fair value consideration, allocation of the purchase price at the end of the measurement period are included in the Company’s Quarterly Report for the quarter ended March 31, 2021. As of September 30, 2021 and December 31, 2020, the remaining estimated contingent consideration was $16.2 million representing the fair value of the remaining annual deferred payments for the year ending December 31, 2021 and the annualized six-month period ending June 30, 2022. As of September 30, 2021, the amounts are included in "Accrued liabilities" on the condensed consolidated balance sheets.

Investments

Investments	9 Months Ended
	Sep. 30, 2021
Schedule of Investments [Abstract]
Investments	Investments Restricted Investments, Held-to-Maturity The following tables present the cost or amortized cost, gross unrealized gains and temporary losses, and estimated fair value of the Company's restricted investments, held-to-maturity: September 30, 2021 Gross Unrealized Cost or Amortized Gains Temporary Estimated Fair Value (In thousands) US corporate securities $ 7,140 $ — $ (6) $ 7,134 Restricted investments, held-to-maturity $ 7,140 $ — $ (6) $ 7,134 December 31, 2020 Gross Unrealized Cost or Amortized Gains Temporary Estimated Fair Value (In thousands) US corporate securities $ 9,001 $ 2 $ (8) $ 8,995 Restricted investments, held-to-maturity $ 9,001 $ 2 $ (8) $ 8,995 As of September 30, 2021, the contractual maturities of the restricted investments, held-to-maturity, were one year or less. There were thirteen securities and sixteen securities that were in an unrealized loss position for less than twelve months as of September 30, 2021 and December 31, 2020, respectively. The Company did not recognize any impairment losses related to its held-to-maturity investments during the quarter or year-to-date periods ended September 30, 2021 or 2020. Embark Convertible Note During the second quarter of 2021, the Company invested $25.0 million in Embark in exchange for a convertible note. The convertible note accrues simple interest on the unpaid principal balance at a rate of 10.0% and is payable on demand any time after April 16, 2022, unless earlier converted into shares of Embark's common stock. The amount outstanding on the convertible note is automatically converted into a number of shares of Embark's common stock upon either the closing of a qualified financing or upon a public event, subject to discounted conversion pricing per share based on a valuation of Embark. On June 22, 2021, Embark and Northern Genesis Acquisition Corp II (NYSE:"NGAB"), a publicly-traded special purpose acquisition company, entered into a definitive business combination agreement that would result in Embark becoming a publicly listed company. Completion of the transaction is expected to occur in the fourth quarter of 2021 and is subject to approval of NGAB stockholders and the satisfaction or waiver of certain other customary closing conditions. Based on the valuation of this public event, the Company estimated that the fair value of this investment was $37.6 million and recognized a $12.6 million gain on the convertible note during the year-to-date period ended September 30, 2021. No gain was recognized during the quarter ended September 30, 2021. Refer to Note 15 for additional information regarding fair value measurements of the Company's investments.

Assets Held for Sale

Assets Held for Sale	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Assets Held For Sale	Assets Held for Sale The Company expects to sell its assets held for sale, which primarily consist of revenue equipment, within the next twelve months. Revenue equipment held for sale totaled $16.7 million and $29.8 million as of September 30, 2021 and December 31, 2020, respectively. The Company had $3.6 million in land and facilities classified as held for sale as of September 30, 2021. No land and facilities were classified as held for sale as of December 31, 2020. Net gains on disposals, including disposals of property and equipment classified as assets held for sale, reported in "Miscellaneous operating expenses" in the condensed consolidated statements of comprehensive income, were: • $22.1 million and $1.7 million for the quarter-to-date periods ended September 30, 2021 and 2020, respectively. • $47.7 million and $6.5 million for the year-to-date periods ended September 30, 2021 and 2020, respectively. The increase in net gains on disposals was primarily due to a stronger market for used revenue equipment during the quarter and year-to-date periods ended September 30, 2021, as compared to the same periods in 2020. The Company did not recognize impairment losses related to assets held for sale during the quarters ended September 30, 2021 and 2020. The Company did not recognize impairment losses during the year-to-date period ended September 30, 2021, as compared to the same period of last year when the Company recognized impairment losses related to assets held for sale of $0.4 million.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill The changes in the carrying amount of goodwill were as follows: (In thousands) Goodwill, balance at December 31, 2020 $ 2,922,964 Adjustments relating to deferred tax assets (7) Acquisitions 1 538,941 Goodwill, balance at September 30, 2021 $ 3,461,898 1 The goodwill associated with the ACT, UTXL and Eleos acquisitions referenced in Note 3 was allocated to the LTL, Logistics, and non-reportable segments, respectively, and is net of purchase price accounting adjustments. The Company did not record any goodwill impairments during the quarter or year-to-date periods ended September 30, 2021 or 2020. Other Intangible Assets Other intangible asset balances were as follows: September 30, 2021 December 31, (In thousands) Definite-lived intangible assets 1 Gross carrying amount $ 1,187,970 $ 894,597 Accumulated amortization (185,304) (145,852) Definite-lived intangible assets, net 1,002,666 748,745 Indefinite-lived trade names: Gross carrying amount 791,258 640,500 Intangible assets, net $ 1,793,924 $ 1,389,245 1 The major categories of the Company's definite-lived intangible assets include customer relationships, non-compete agreements, internally-developed software, trade names, and others. Identifiable intangible assets subject to amortization have been recorded at fair value. Intangible assets related to acquisitions other than the 2017 Merger are amortized over a weighted-average amortization period of 18.9 years. The Company's customer relationship intangible assets related to the 2017 Merger are being amortized over a weighted average amortization period of 19.9 years. As of September 30, 2021, management anticipates that the composition and amount of amortization associated with intangible assets will be $15.9 million for the remainder of 2021, $62.8 million in 2022, $62.2 million for each of the years 2023 and 2024, and $62.1 million in 2025. Actual amounts of amortization expense may differ from estimated amounts due to additional intangible asset acquisitions, impairment of intangible assets, accelerated amortization of intangible assets, and other events.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Effective Tax Rate — The quarter-to-date September 30, 2021 and September 30, 2020 effective tax rates were 22.8% and 28.1%, respectively. The year-to-date September 30, 2021 and September 30, 2020 effective tax rates were 24.4% and 27.0%, respectively. Valuation Allowance — The Company has not established a valuation allowance as it has been determined that, based upon available evidence, a valuation allowance is not required. Management believes that it is more likely than not that the results of future operations will generate sufficient taxable income to realize the deferred tax assets. Unrecognized Tax Benefits — Management believes it is reasonably possible that a decrease of up to $0.6 million in unrecognized tax benefits relating to federal deductions may be necessary within the next twelve months. Interest and Penalties — Accrued interest and penalties related to unrecognized tax benefits were approximately $0.1 million and $0.3 million as of September 30, 2021 and December 31, 2020, respectively. Tax Examinations — Certain of the Company's subsidiaries are currently under examination by various state jurisdictions for tax years ranging from 2014 to 2019 . At the completion of these examinations, management does not expect any adjustments that would have a material impact on the Company's effective tax rate. Years subsequent to 2015 remain subject to examination.

Accounts Receivable Securitizat

Accounts Receivable Securitization	9 Months Ended
	Sep. 30, 2021
Transfers and Servicing [Abstract]
Accounts Receivable Securitization	Accounts Receivable Securitization On April 23, 2021, the Company entered into the 2021 RSA which further amended the 2018 RSA. The 2021 RSA is a secured borrowing that is collateralized by the Company's eligible receivables, for which the Company is the servicing agent. The Company's receivable originator subsidiaries sell, on a revolving basis, undivided interests in all of their eligible accounts receivable to Swift Receivables Company II, LLC ("SRCII") who in turn sells a variable percentage ownership in those receivables to the various purchasers. The Company's eligible receivables are included in "Trade receivables, net of allowance for doubtful accounts" in the condensed consolidated balance sheets. As of September 30, 2021, the Company's eligible receivables generally have high credit quality, as determined by the obligor's corporate credit rating. The 2021 RSA is subject to fees, various affirmative and negative covenants, representations and warranties, and default and termination provisions customary for facilities of this type. The Company was in compliance with these covenants as of September 30, 2021. Collections on the underlying receivables by the Company are held for the benefit of SRCII and the various purchasers and are unavailable to satisfy claims of the Company and its subsidiaries. The following table summarizes the key terms of the 2021 RSA and 2018 RSA (dollars in thousands): 2021 RSA 2018 RSA Effective date April 23, 2021 July 11, 2018 Final maturity date April 23, 2024 July 9, 2021 Borrowing capacity $400,000 $325,000 Accordion option 1 $100,000 $175,000 Unused commitment fee rate 2 20 to 40 basis points 20 to 40 basis points Program fees on outstanding balances 3 4 one-month LIBOR + 82.5 basis points one-month LIBOR + 80 to 100 basis points 1 The accordion option increases the maximum borrowing capacity, subject to participation of the purchasers. 2 The 2021 RSA and 2018 RSA commitment fees rate are based on the percentage of the maximum borrowing capacity utilized. 3 Only the rate for the 2018 RSA program fee is subject to the Company's consolidated total net leverage ratio. 4 As identified within the 2021 RSA, the lender can trigger an amendment by identifying and deciding upon a replacement for LIBOR. Availability under the 2021 RSA and 2018 RSA is calculated as follows: 2021 RSA 2018 RSA September 30, 2021 December 31, 2020 (In thousands) Borrowing base, based on eligible receivables $ 400,000 $ 302,700 Less: outstanding borrowings 1 (279,000) (214,000) Less: outstanding letters of credit, net (65,300) (67,281) Availability under accounts receivable securitization facilities $ 55,700 $ 21,419 1 As of September 30, 2021, outstanding borrowings are included in "Accounts receivable securitization – less current portion" in the condensed consolidated balance sheets and are offset by $0.6 million of deferred loan costs. As of December 31, 2020, outstanding borrowings are included in "Accounts receivable securitization – current portion" in the condensed consolidated balance sheets and are offset by $0.1 million of deferred loan costs . Interest accrued on the aggregate principal balance at a rate of 0.9% and 1.0% as of September 30, 2021 and December 31, 2020, respectively.

Debt And Financing

Debt And Financing	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Debt Disclosure	Debt and Financing Other than the Company's accounts receivable securitization as discussed in Note 8, the Company's long-term debt consisted of the following: September 30, 2021 December 31, 2020 (In thousands) 2021 Term Loan A-1, due December 3, 2022, net 1 2 $ 199,588 $ — 2021 Term Loan A-2, due September 3, 2024, net 1 2 199,571 — 2021 Term Loan A-3, due September 3, 2026, net 1 2 798,264 — 2017 Term Loan, due October 2022, net 1 3 — 298,907 2021 Prudential Notes, net 47,760 — Other 5,567 — Total long-term debt, including current portion 1,250,750 298,907 Less: current portion of long-term debt (12,728) — Long-term debt, less current portion $ 1,238,022 $ 298,907 September 30, 2021 December 31, 2020 (In thousands) Total long-term debt, including current portion $ 1,250,750 $ 298,907 2021 Revolver, due September 3, 2026 1 4 300,000 — 2017 Revolver, due October 2022 1 5 — 210,000 Long-term debt, including revolving line of credit $ 1,550,750 $ 508,907 1 Refer to Note 15 for information regarding the fair value of debt. 2 The carrying amounts of the 2021 Term Loan A-1, 2021 Term Loan A-2, and 2021 Term Loan A-3 are net of $0.4 million, $0.4 million, and $1.7 million in deferred loan costs as of September 30, 2021, respectively. 3 Net of $1.1 million deferred loan costs at December 31, 2020. 4 The Company also had outstanding letters of credit of $63.8 million under the 2021 Revolver, primarily related to workers' compensation and self-insurance liabilities at September 30, 2021. Subsequent to September 30, 2021, we paid $95.0 million on the 2021 Revolver. 5 The Company also had outstanding letters of credit of $29.3 million under the 2017 Revolver, primarily related to workers' compensation and self-insurance liabilities at December 31, 2020. Credit Agreements 2021 Debt Agreement — On September 3, 2021, the Company entered into the $2.3 billion 2021 Debt Agreement (an unsecured credit facility), with a group of banks, replacing the 2017 Debt Agreement and the July 2021 Term Loan (described below). The following table presents the key terms of the 2021 Debt Agreement: 2021 Term Loan A-1 2021 Term Loan A-2 2021 Term Loan A-3 2021 Revolver 2 2021 Debt Agreement Terms (Dollars in thousands) Maximum borrowing capacity $200,000 $200,000 $800,000 $1,100,000 Final maturity date December 3, 2022 September 3, 2024 September 3, 2026 September 3, 2026 Interest rate minimum margin BSBY BSBY BSBY BSBY Interest rate minimum margin 1 0.75% 0.75% 0.88% 0.88% Interest rate maximum margin 1 1.38% 1.38% 1.50% 1.50% Minimum principal payment — amount $— $— $10,000 $— Minimum principal payment — frequency Once Once Quarterly Once Minimum principal payment — commencement date December 3, 2022 September 3, 2024 September 30, 2024 September 3, 2026 1 The interest rate margin for the 2021 Term Loans and 2021 Revolver is based on the Company's consolidated leverage ratio. As of September 30, 2021, interest accrued at 1.1% on the 2021 Term Loans and 1.2% on the 2021 Revolver. 2 The commitment fee for the unused portion of the 2021 Revolver is based on the Company's consolidated leverage ratio, and ranges from 0.1% to 0.2%. As of September 30, 2021, commitment fees on the unused portion of the 2021 Revolver accrued at 0.1% and outstanding letter of credit fees accrued at 1.1%. Pursuant to the 2021 Debt Agreement, the 2021 Revolver and the 2021 Term Loans contain certain financial covenants with respect to a maximum net leverage ratio and a minimum consolidated interest coverage ratio. The 2021 Debt Agreement provides flexibility regarding the use of proceeds from asset sales, payment of dividends, stock repurchases, and equipment financing. In addition to the financial covenants, the 2021 Debt Agreement includes usual and customary events of default for a facility of this nature and provides that, upon the occurrence and continuation of an event of default, payment of all amounts payable under the 2021 Debt Agreement may be accelerated, and the lenders' commitments may be terminated. The 2021 Debt Agreement contains certain usual and customary restrictions and covenants relating to, among other things, dividends (which are restricted only if a default or event of default occurs and is continuing or would result therefrom), liens, affiliate transactions, and other indebtedness. As of September 30, 2021, the Company was in compliance with the covenants under the 2021 Debt Agreement. Borrowings under the 2021 Debt Agreement, are made by Knight-Swift Transportation Holdings Inc., and are guaranteed by certain of the Company's domestic subsidiaries (other than its captive insurance subsidiaries, driving academy subsidiary, and bankruptcy-remote special purpose subsidiary). July 2021 Term Loan — On July 6, 2021, Knight-Swift entered into a $1.2 billion term loan with Bank of America, N.A (the "July 2021 Term Loan"). The July 2021 Term Loan was incremental to, and was separate from, the 2017 Debt Agreement. The July 2021 Term Loan was fully funded on July 6, 2021 and there were no scheduled principal payments prior to its maturity in October 2022. The interest rate applicable to the July 2021 Term Loan was subject to a leverage-based grid and equaled the BSBY rate plus 1.000% at closing. The July 2021 Term Loan was paid off and terminated using the proceeds of the 2021 Term Loans, discussed above. The July 2021 Term Loan contained similar terms to the 2017 Debt Agreement, including the financial covenants, usual and customary events of default for a facility of this nature, and certain usual and customary restrictions and covenants. ACT Credit Agreement Prudential Notes — Through the acquisition of ACT, the Company assumed the S econd Amended and Restated Note Purchase and Private Shelf Agreement with Prudential Capital Group ("2014 Prudential Notes"). On September 3, 2021, ACT entered into the 2021 Prudential Notes, replacing the 2014 Prudential Notes. The 2021 Prudential Notes have interest rates ranging from 4.05% to 4.40% and various maturity dates ranging from October 2023 through January 2028. The 2021 Prudential Notes allow ACT to borrow up to $125 million, less amounts then currently outstanding with Prudential Capital Group, provided that certain financial ratios are maintained. The 2021 Prudential Notes are unsecured and contain usual and customary restrictions on, among other things, the ability to make certain payments to stockholders, similar to the provisions of the Company's 2021 Debt Agreement. As of September 30, 2021, ACT had $77.1 million available under the agreement. See Note 15 for fair value disclosures regarding the Company's debt instruments.

Defined Benefit Pension Plan

Defined Benefit Pension Plan	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Defined Benefit Plan	Defined Benefit Pension Plan Through the ACT Acquisition, the Company assumed a defined benefit pension plan covering ACT's drivers, drivers' helpers, warehousemen, warehousemen's helpers, mechanics, and mechanics' helpers. The plan provides normal retirement benefits based on years of credited service and applicable benefit units as defined by the plan. Provision is also made for early and defined retirements. The pension plan was amended such that benefit accrual and plan participation for the plan were effectively frozen as of January 1, 1997, resulting in a curtailment on that date. The net pension liability recognized is as follows: September 30, 2021 (In thousands) Projected benefit obligation $ 71,263 Less: fair value of plan assets 69,400 Unfunded status 1,863 Accrued pension liability recognized 1 $ 1,863 1 The pension liability is included in "Other long-term liabilities" in the condensed consolidated balance sheets. "Other comprehensive loss" in the condensed consolidated statements of comprehensive income included a $0.9 million loss from pension plan adjustments during the third quarter of 2021. The provisions of the plan do not require compensation levels to be considered in determining the plan’s benefit obligation. As such, the accumulated benefit obligation and projected benefit obligation are the same. Other information concerning the defined benefit pension plan is summarized below: Quarter-to-Date September 30, 2021 (In thousands) Net periodic pension income $ 596 Benefits paid 771 Assumptions A weighted-average discount rate of 2.53% was used to determine benefit obligations as of September 30, 2021. The following weighted-average assumptions were used to determine net periodic pension cost: Quarter-to-Date September 30, 2021 Discount rate 2.49 % Expected long-term rate of return on pension plan assets 6.00 % ACT's assumptions for the expected long-term rate of return on pension plan assets are based on a periodic review of the plan’s asset allocation over a long-term period. Expectations of returns for each asset class are based on comprehensive reviews of historical data and economic/financial market theory. The expected long-term rate of return on pension plan assets was selected from within the reasonable range of rates determined by (1) historical real returns, net of inflation, for the asset classes covered by the investment policy and (2) projections of inflation over the long-term period during which benefits are payable to plan participants. The defined benefit pension plan weighted-average asset allocations, by asset category, are as follows: September 30, 2021 Asset category: Equity securities 30 % Debt securities 69 % Cash and cash equivalents 1 % Total 100 % Pension plan assets The target allocation by asset category, is as follows: September 30, 2021 Asset category: Equity securities 30 % Debt securities 70 % Total 100 % The investment policy includes various guidelines and procedures designed to ensure assets are invested in a manner necessary to meet expected future benefit payments. The investment guidelines consider a broad range of economic conditions. Central to the policy are target allocation percentages (shown above) by major asset categories. The objectives of the target allocation percentages are to maintain investment portfolios that diversify risk through prudent asset allocation parameters and achieve asset returns that meet or exceed the plan’s actuarial assumptions. Refer to Note 15 for additional information regarding fair value measurements of the Company's investments. Cash flows ACT did not contribute to the pension plan in the quarter-to-date period ended September 30, 2021. ACT is not expecting to recognize any net loss in net other comprehensive losses during the remainder of 2021 or 2022. The following benefit payments are expected to be paid in each of the fiscal years as follows: September 30, 2021 (In thousands) Remainder of 2021 $ 874 2022 3,593 2023 3,707 2024 3,851 2025 3,953 2026 4,040 2027 through 2030 16,453 Total $ 36,471

Commitments

Commitments	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments	Commitments Purchase Commitments As of September 30, 2021, the Company had outstanding commitments to purchase revenue equipment of $256.7 million in the remainder of 2021 ($166.8 million of which were tractor commitments), $65.9 million in 2022 ($7.5 million of which were tractor commitments), and none thereafter. These purchases may be financed through any combination of operating leases, finance leases, debt, proceeds from sales of existing equipment, and cash flows from operations. As of September 30, 2021, the Company had outstanding commitments to purchase facilities and non-revenue equipment of $39.0 million in the remainder of 2021, $4.9 million in the two-year period 2022 through 2023, $0.8 million in the two-year period 2024 through 2025, and none thereafter. Factors such as costs and opportunities for future terminal expansions may change the amount of such expenditures. As of September 30, 2021, the Company had outstanding commitments for fuel purchases of $3.6 million in the remainder of 2021, and none thereafter. TRP Commitments Since 2003, Knight has entered into partnership agreements with entities that make privately-negotiated equity investments. In these agreements, Knight committed to invest in return for an ownership percentage. During the first quarter of 2021, Knight increased its commitment to invest in TRP Capital Partners V, LP by $10.0 million to $30.0 million, with $20.5 million outstanding as of September 30, 2021. There were no other material changes related to the previously disclosed TRP commitments during the quarter ended September 30, 2021. Embark Commitment On June 23, 2021, the Company entered into a stock subscription agreement with Embark to purchase $25.0 million of Embark's common stock, with $25.0 million outstanding as of September 30, 2021.

Contingencies and Legal Proceed

Contingencies and Legal Proceedings	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Legal Proceedings	Contingencies and Legal Proceedings Legal Proceedings Information is provided below regarding the nature, status, and contingent loss amounts, if any, associated with the Company's pending legal matters. There are inherent uncertainties in these legal matters, some of which are beyond management's control, making the ultimate outcomes difficult to predict. Moreover, management's views and estimates related to these matters may change in the future, as new events and circumstances arise and the matters continue to develop. The Company has made accruals with respect to its legal matters where appropriate, which are included in "Accrued liabilities" in the condensed consolidated balance sheets. The Company has recorded an aggregate accrual of approximately $18.4 million, relating to the Company's outstanding legal proceedings as of September 30, 2021. Based on management's present knowledge of the facts and (in certain cases) advice of outside counsel, management does not believe that loss contingencies arising from pending matters are likely to have a material adverse effect on the Company's overall financial position, operating results, or cash flows after taking into account any existing accruals. However, actual outcomes could be material to the Company's financial position, operating results, or cash flows for any particular period. EMPLOYEE COMPENSATION AND PAY PRACTICES MATTERS CRST Expedited The plaintiff alleges tortious interference with contract and unjust enrichment related to non-competition agreements entered into with certain of its drivers. Plaintiff(s) Defendant(s) Date instituted Court or agency currently pending in CRST Expedited, Inc. Swift Transportation Co. of Arizona LLC. March 20, 2017 United States District Court for the Northern District of Iowa Recent Developments and Current Status In July 2019, a jury issued an adverse verdict in this lawsuit. The court issued a decision granting in part and denying in part certain motions related to the jury’s verdict. Both parties have appealed the court’s decision. On August 6, 2021 a three-judge panel of the 8th Circuit Court of Appeals issued an opinion reversing the trial court’s decision. On October 4, 2021 the 8th Circuit Court of Appeals denied a petition for rehearing. The likelihood that a loss has been incurred is no longer probable, and the accrual for this lawsuit has accordingly been reversed as of September 30, 2021. California Wage, Meal, and Rest Class Actions The plaintiffs generally allege one or more of the following: that the Company 1) failed to pay the California minimum wage; 2) failed to provide proper meal and rest periods; 3) failed to timely pay wages upon separation from employment; 4) failed to pay for all hours worked; 5) failed to pay overtime; 6) failed to properly reimburse work-related expenses; and 7) failed to provide accurate wage statements. Plaintiff(s) Defendant(s) Date instituted Court or agency currently pending in John Burnell 1 Swift Transportation Co., Inc March 22, 2010 United States District Court for the Central District of California James R. Rudsell 1 Swift Transportation Co. of Arizona, LLC and Swift Transportation Company April 5, 2012 United States District Court for the Central District of California Recent Developments and Current Status In April 2019, the parties reached settlement of this matter. In January 2020, the court granted final approval of the settlement. Two objectors appealed the court’s decision granting final approval of the settlement. The likelihood that a loss has been incurred is probable and estimable, and the loss has accordingly been accrued as of September 30, 2021. INDEPENDENT CONTRACTOR MATTERS Ninth Circuit Independent Contractor Misclassification Class Action The putative class alleges that Swift misclassified independent contractors as independent contractors, instead of employees, in violation of the Fair Labor Standards Act and various state laws. The lawsuit also raises certain related issues with respect to the lease agreements that certain independent contractors have entered into with Interstate Equipment Leasing, LLC. The putative class seeks unpaid wages, liquidated damages, interest, other costs, and attorneys' fees. Plaintiff(s) Defendant(s) Date instituted Court or agency currently pending in Joseph Sheer, Virginia Van Dusen, Jose Motolinia, Vickii Schwalm, Peter Wood 1 Swift Transportation Co., Inc., Interstate Equipment Leasing, Inc., Jerry Moyes, and Chad Killebrew December 22, 2009 Unites States District Court of Arizona and Ninth Circuit Court of Appeals Recent Developments and Current Status In January 2020, the court granted final approval of the settlement in this matter. In March 2020, the Company paid the settlement amount approved by the court. As of September 30, 2021, the Company has accrued for anticipated costs associated with finalizing this matter. 1 Individually and on behalf of all others similarly situated. Other Environmental The Company's tractors and trailers are involved in motor vehicle accidents, experience damage, mechanical failures and cargo issues as an incidental part of its normal ordinary course of operations. From time to time, these matters result in the discharge of diesel fuel, motor oil or other hazardous materials into the environment. Depending on local regulations and who is determined to be at fault, the Company is sometimes responsible for the clean-up costs associated with these discharges. As of September 30, 2021, the Company's estimate for its total legal liability for all such clean-up and remediation costs was approximately $0.4 million in the aggregate for all current and prior year claims. Self Insurance Swift and Knight • Automobile Liability, General Liability, and Excess Liability — Effective November 1, 2020, the Company has $100.0 million in excess auto liability ("AL") coverage. Effective November 1, 2019, the Company had $130.0 million in excess AL coverage. For prior years, Swift and Knight separately maintained varying excess AL and general liability limits. During prior policy periods, Swift AL claims were subject to a $10.0 million self-insured retention ("SIR") per occurrence and Knight AL claims were subject to a $1.0 million to $3.0 million SIR per occurrence. Additionally, Knight carried a $2.5 million aggregate deductible for any loss or losses within the $5.0 million excess of $5.0 million layer of coverage. Effective March 1, 2020, Knight and Swift retain the same $10.0 million SIR per occurrence. • Cargo Damage and Loss — The Company is insured against cargo damage and loss with liability limits of $2.0 million per truck or trailer with a $10.0 million limit per occurrence. • Workers' Compensation and Employers' Liability — The Company is self-insured for workers' compensation coverage. Swift maintains statutory coverage limits, subject to a $5.0 million SIR for each accident or disease. Effective March 1, 2019, Knight maintains statutory coverage limits, subject to a $2.0 million SIR for each accident or disease. • Medical — Knight maintains primary and excess coverage for employee medical expenses, with a $0.4 million SIR per claimant. Effective January 1, 2020, Swift provides primary and excess coverage for employee medical expenses, with an SIR of $0.5 million per claimant to all employees. ACT — ACT maintains SIRs for claims on cargo losses, employee health and welfare, bodily injury and property, general liability and workers’ compensation. Losses under the employee health and welfare, BIPD, and workers’ compensation programs are typically limited on a per claim and aggregate basis through stop-loss and excess insurance policies. Risk retention amounts per occurrence are as follows: • Workers' compensation - $1.0 million • Bodily injury and property damage - $2.0 million (ACT maintains a $5.0 million annual corridor deductible subject to a $10.0 million three-year policy term aggregate cap.) • Employee medical - $1.0 million

Share Repurchase Plans

Share Repurchase Plans	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Share Repurchase Plan	Share Repurchase Plans On November 30, 2020, the Company announced that the Board approved the repurchase of up to $250.0 million worth of the Company's outstanding common stock (the "2020 Knight-Swift Share Repurchase Plan"). With the adoption of the 2020 Knight-Swift Share Repurchase Plan, the Company terminated the previous share repurchase plan, which had approximately $54.1 million of authorized purchases remaining upon termination. The following table presents the Company's repurchases of its common stock under the respective share repurchase plans, excluding advisory fees: Share Repurchase Plan Quarter-to-Date September 30, 2021 Year-to-Date September 30, 2021 Board Approval Date Authorized Amount Shares Amount Shares Amount (shares and dollars in thousands) November 24, 2020 1 $250,000 — $ — 1,303 $ 53,661 Quarter-to-Date September 30, 2020 Year-to-Date September 30, 2020 May 30, 2019 $250,000 — $ — 1,139 $ 34,630 1 $196.3 million and $250.0 million remained available under the 2020 Knight-Swift Share Repurchase Plan as of September 30, 2021 and December 31, 2020, respectively.

Weighted Average Shares Outstan

Weighted Average Shares Outstanding	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Weighted Average Shares Outstanding	Weighted Average Shares Outstanding Earnings per share, basic and diluted, as presented in the condensed consolidated statements of comprehensive income, are calculated by dividing net income attributable to Knight-Swift by the respective weighted average common shares outstanding during the period. The following table reconciles basic weighted average shares outstanding to diluted weighted average shares outstanding: Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 (In thousands) Basic weighted average common shares outstanding 165,966 170,205 165,823 170,257 Dilutive effect of equity awards 1,140 823 1,113 778 Diluted weighted average common shares outstanding 167,106 171,028 166,936 171,035 Anti-dilutive shares excluded from diluted earnings per share 1 23 8 165 187 1 Shares were excluded from the dilutive-effect calculation because the outstanding awards' exercise prices were greater than the average market price of the Company's common stock for the periods presented.

Fair Value Measurement

Fair Value Measurement	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurement	Fair Value Measurement ASC Topic 820, Fair Value Measurements and Disclosures, requires that the Company disclose estimated fair values for its financial instruments. The estimated fair value of a financial instrument is the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date in the principal or most advantageous market for the asset or liability. Fair value estimates are made at a specific point in time and are based on relevant market information and information about the financial instrument. These estimates do not reflect any premium or discount that could result from offering for sale at one time the Company's entire holdings of a particular financial instrument. Changes in assumptions could significantly affect these estimates. Because the fair value is estimated as of September 30, 2021 and December 31, 2020, the amounts that will actually be realized or paid at settlement or maturity of the instruments in the future could be significantly different. The estimated fair values of the Company's financial instruments represent management's best estimates of the amounts that would be received to sell those assets or that would be paid to transfer those liabilities in an orderly transaction between market participants at that date. The estimated fair value measurements maximize the use of observable inputs. However, in situations where there is little, if any, market activity for the asset or liability at the measurement date, the estimated fair value measurement reflects management's own judgments about the assumptions that market participants would use in pricing the asset or liability. These judgments are developed by the Company based on the best information available under the circumstances. The following summary presents a description of the methods and assumptions used to estimate the fair value of each class of financial instrument. Restricted Investments, Held-to-Maturity — The estimated fair value of the Company's restricted investments, held-to-maturity, is based on quoted prices in active markets that are readily and regularly obtainable. See Note 4 for additional disclosures regarding restricted investments, held-to-maturity. Convertible Notes — The estimated fair value of the Company's convertible note is based on probability weighted discounted cash flow analysis of the corresponding pay-off/redemption. Equity Method Investments — The estimated fair value of the Company's equity method investments are privately negotiated investments. The carrying amount of these investments approximates the fair value. Equity Securities — The estimated fair value of the Company's investments in equity securities is based on quoted prices in active markets that are readily and regularly obtainable. Pension Plan Assets — The estimated fair value of ACT's pension plan assets are based on quoted prices in active markets that are readily and regularly obtainable. Debt Instruments and Leases — For notes payable under the 2017 Revolver, the 2017 Term Loan, the 2021 Revolver and the 2021 Term Loans, fair value approximates the carrying value due to the variable interest rate. The carrying values of the 2021 RSA and 2018 RSA approximate fair value, as the underlying receivables are short-term in nature and only eligible receivables (such as those with high credit ratings) are qualified to secure the borrowed amounts. For finance and operating lease liabilities, the carrying value approximates the fair value, as the Company's finance and operating lease liabilities are structured to amortize in a manner similar to the depreciation of the underlying assets. Contingent Consideration — The estimated fair value of the Company's contingent consideration owed to sellers is calculated using applicable models and inputs for each acquiree. Other — Cash and cash equivalents, restricted cash, net accounts receivable, income tax refund receivable, and accounts payable represent financial instruments for which the carrying amount approximates fair value, as they are short-term in nature. These instruments are accordingly excluded from the disclosures below. All remaining balance sheet amounts excluded from the below are not considered financial instruments, subject to this disclosure. The following table presents the carrying amounts and estimated fair values of the Company's major categories of financial assets and liabilities: September 30, 2021 December 31, 2020 Condensed Consolidated Balance Sheets Caption Carrying Estimated Carrying Estimated (In thousands) Financial Assets: Restricted investments, held-to-maturity 1 Restricted investments, held-to-maturity, amortized cost $ 7,140 $ 7,134 $ 9,001 $ 8,995 Equity method investments Other long-term assets 82,883 82,883 77,562 77,562 Investments in equity securities Other long-term assets 21,063 21,063 18,675 18,675 Convertible note Other current assets 37,631 37,631 — — Financial Liabilities: 2017 Term Loan, due October 2022 2 Long-term debt – less current portion $ — $ — $ 298,907 $ 300,000 2021 Term Loan A-1, due December 2022 3 Long-term debt – less current portion 199,588 200,000 — — 2021 Term Loan A-2, due September, 2024 3 Long-term debt – less current portion 199,571 200,000 — — 2021 Term Loan A-3, due September 2026 3 Long-term debt – less current portion 798,264 800,000 — — 2018 RSA, due July 2021 4 Accounts receivable securitization — — 213,918 214,000 2021 RSA, due April 2024 5 Accounts receivable securitization 278,428 279,000 — — 2017 Revolver, due October 2022 Revolving line of credit — — 210,000 210,000 2021 Revolver, due September 2026 Revolving line of credit 300,000 300,000 — — 2021 Prudential Notes 6 Finance lease liabilities and long-term debt 47,760 50,321 — — Contingent consideration, acquisitions Accrued liabilities, Other long-term liabilities 21,200 21,200 16,200 16,200 1 Refer to Note 4 for the differences between the carrying amounts and estimated fair values of the Company's restricted investments, held-to-maturity. 2 The carrying amount of the 2017 Term Loan is net of $1.1 million in deferred loan costs as of December 31, 2020. 3 The carrying amounts of the 2021 Term Loan A-1, 2021 Term Loan A-2, and 2021 Term Loan A-3 are net of $0.4 million, $0.4 million, and $1.7 million in deferred loan costs as of September 30, 2021, respectively. 4 The carrying amount of the 2018 RSA is net of $0.1 million in deferred loan costs as of December 31, 2020 . 5 The carrying amount of the 2021 RSA is net of $0.6 million in deferred loan costs as of September 30, 2021 . 6 The carrying amount of the 2021 Prudential Notes is net of $0.1 million in deferred loan costs and $2.4 million in fair value adjustments as of September 30, 2021 . Recurring Fair Value Measurements (Assets) — The following table depicts the level in the fair value hierarchy of the inputs used to estimate the fair value of assets measured on a recurring basis as of September 30, 2021 and December 31, 2020 : Fair Value Measurements at Reporting Date Using: Estimated Level 1 Inputs Level 2 Inputs Level 3 Inputs Unrealized Gain Position (In thousands) As of September 30, 2021 Convertible note 1 $ 37,631 $ — $ — $ 37,631 $ 12,631 Investments in equity securities 2 $ 21,063 $ 21,063 $ — $ — $ 11,135 As of December 31, 2020 Investments in equity securities 3 $ 18,675 $ 18,675 $ — $ — $ 3,553 1 The Company recognized $12.6 million of unrealized gains on the convertible note for the year-to-date period ended September 30, 2021, which is included within "Other income, net" within the condensed consolidated statement of comprehensive income. The fair value of the note was determined using a discounted cash flow analysis based on the probability of exit event options and exit event dates. 2 Fair value activity from the investments in equity securities is recorded in "Other income, net" within the condensed consolidated statement of comprehensive income. • During the quarter ended September 30, 2021, the Company recognized $4.0 million in gains on these investments in equity securities, consisting of $3.0 million in unrealized gains and $1.0 million in realized gains. • During the year-to-date period ended September 30, 2021, the Company recognized $12.8 million in gains on these investments in equity securities, consisting of $7.6 million in unrealized gains and $5.2 million in realized gains. 3 Fair value activity from the investments in equity securities is recorded in "Other income, net" within the condensed consolidated statement of comprehensive income. • During the quarter ended September 30, 2020, the Company recognized $4.4 million in unrealized gains on these investments in equity securities. • During the year-to-date period ended September 30, 2020, the Company recognized $6.9 million in unrealized gains on these investments in equity securities. Recurring Fair Value Measurements (Liabilities) — The following table depicts the level in the fair value hierarchy of the inputs used to estimate the fair value of liabilities measured on a recurring basis as of September 30, 2021 and December 31, 2020: Fair Value Measurements at Reporting Date Using: Estimated Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Gain (Loss) (In thousands) As of September 30, 2021 Contingent consideration associated with acquisitions 1 $ 21,200 $ — $ — $ 21,200 $ — As of December 31, 2020 Contingent consideration associated with acquisition 2 $ 16,200 $ — $ — $ 16,200 $ (6,730) 1 The Company did not recognize any gains (losses) during the quarter or year-to-date periods ended September 30, 2021 related to the revaluation of these liabilities. Refer to Note 3 for information regarding the components of these liabilities. 2 During the fourth quarter of 2020, the Company increased the estimated fair value of the remaining contingent consideration representing the final two annual payments, resulting in a $6.7 million fair value adjustment of the deferred earnout, which was recorded in “Miscellaneous operating expenses” in the consolidated statement of comprehensive income. The Company did not recognize any losses during the quarter and year-to-date periods ended September 30, 2020. Nonrecurring Fair Value Measurements (Assets) — As of September 30, 2021, the Company had no major categories of assets estimated at fair value that were measured on a nonrecurring basis. The following table depicts the level in the fair value hierarchy of the inputs used to estimate fair value of assets measured on a nonrecurring basis as of December 31, 2020: Fair Value Measurements at Reporting Date Using: Estimated Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Loss (In thousands) As of December 31, 2020 Equipment 1 5,851 — 5,851 — (5,335) 1 Reflects the non-cash impairment of certain alternative fuel technology (within the non-reportable segments) and certain revenue equipment held for sale (within the Truckload segment). The Company did not recognize any impairments during the quarter ended September 30, 2020. The Company recognized $1.3 million of impairments during the year-to-date period ended September 30, 2020. Nonrecurring Fair Value Measurements (Liabilities) — As of September 30, 2021 and December 31, 2020, the Company had no major categories of liabilities estimated at fair value that were measured on a nonrecurring basis. Fair Value of Pension Plan Assets — The following table sets forth by level the fair value hierarchy of ACT's pension plan financial assets accounted for at fair value on a recurring basis. Assets are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. ACT's assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect the valuation of fair value assets and their placement within the fair value hierarchy levels. Fair Value Measurements at Reporting Date Using: Estimated Level 1 Inputs Level 2 Inputs Level 3 Inputs (In thousands) As of September 30, 2021 US equity funds $ 14,810 $ 14,810 $ — $ — International equity funds 6,184 6,184 — — Fixed income funds 47,583 47,583 — — Cash and cash equivalents 823 823 — — Total pension plan assets $ 69,400 $ 69,400 $ — $ —

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions The following table presents Knight-Swift's transactions with companies controlled by and/or affiliated with its related parties: Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 Provided by Knight-Swift Received by Knight-Swift Provided by Knight-Swift Received by Knight-Swift Provided by Knight-Swift Received by Knight-Swift Provided by Knight-Swift Received by Knight-Swift (In thousands) Freight Services: Central Freight Lines 1 $ — $ — $ 1 $ — $ — $ — $ 7,837 $ — SME Industries 1 — — 28 — — — 56 — Total $ — $ — $ 29 $ — $ — $ — $ 7,893 $ — Facility and Equipment Leases: Central Freight Lines 1 $ — $ — $ 25 $ 92 $ — $ — $ 48 $ 277 Other Affiliates 1 — 69 2 37 — 214 11 146 Total $ — $ 69 $ 27 $ 129 $ — $ 214 $ 59 $ 423 Other Services: Central Freight Lines 1 $ — $ — $ 412 $ — $ — $ — $ 427 $ — DPF Mobile 1 — — — 2 — — — 33 Other Affiliates 1 8 9 13 — 21 27 32 — Total $ 8 $ 9 $ 425 $ 2 $ 21 $ 27 $ 459 $ 33 1 Entities affiliated with former Board member Jerry Moyes include Central Freight Lines, SME Industries, and DPF Mobile. "Other affiliates" includes entities that are associated with various board members and executives and require approval by the Board prior to completing transactions. Transactions with these entities generally include freight services, facility and equipment leases, equipment sales, and other services. • Freight Services Provided by Knight-Swift — The Company charges each of these companies for transportation services. • Freight Services Received by Knight-Swift — Transportation services received from Central Freight Lines represent less-than-truckload freight services rendered to haul parts and equipment to Company shop locations. • Other Services Provided by Knight-Swift — Other services provided by the Company to the identified related parties include equipment sales and miscellaneous services. • Other Services Received by Knight-Swift — Consulting fees, diesel particulate filter cleaning, sales of various parts and tractor accessories, and certain third-party payroll and employee benefits administration services from the identified related parties are included in other services received by the Company. During the quarter ended September 30, 2020, the ownership percentage of Jerry Moyes and related affiliates fell below the threshold requiring related party disclosure. The amounts included in this Note 16 pertain to transactions that occurred prior to the date that the ownership percentage changed. Receivables and payables pertaining to related party transactions were: September 30, 2021 December 31, 2020 Receivable Payable Receivable Payable (In thousands) Central Freight Lines $ — $ — $ 133 $ — DPF Mobile — — — 41 Other Affiliates 6 44 2 10 Total $ 6 $ 44 $ 135 $ 51

Information by Segment and Geog

Information by Segment and Geography	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Information by Segment and Geography	Information by Segment and Geography Segment Information The Company has four reportable segments: Truckload, Logistics, Intermodal, and LTL, as well as the non-reportable segments, discussed below. Based on how economic factors affect the nature, amount, timing, and uncertainty of revenue or cash flows, the Company disaggregates revenues by reportable segment for the purposes of applying ASC Topic 606, Revenue from Contracts with Customers. The Company's twenty-three operating segments are structured around the types of transportation service offerings provided to our customers, as well as the equipment utilized. In addition, the operating segments may be further distinguished by the Company’s respective brands. The Company aggregated these various operating segments into the four reportable segments discussed below based on similarities with both their qualitative and economic characteristics. Truckload The Truckload reportable segment is comprised of nine truckload operating segments that provide similar transportation services to the Company's customers utilizing similar transportation equipment over both irregular (one-way movement) and/or dedicated routes. The Truckload reportable segment consists of irregular route and dedicated, refrigerated, expedited, flatbed, and cross-border operations. Logistics The Logistics reportable segment is comprised of six logistics operating segments that provide similar transportation services to the Company's customers and primarily consist of brokerage and other freight management services utilizing third-party transportation providers and their equipment. Intermodal The Intermodal reportable segment is comprised of two intermodal operating segments that provide similar transportation services to the Company's customers. These transportation services include arranging the movement of customers' freight through third-party intermodal rail services on the Company’s trailing equipment (trailers on flat cars and rail containers), as well as drayage services to transport loads between the railheads and customer locations. LTL The LTL reportable segment is comprised of one operating segment and provides our customers with regional LTL transportation services through a network of over 70 service centers in the Company's geographical footprint. The Company's LTL service also includes national coverage to customers by utilizing partner carriers for areas outside of the Company's direct network. Non-reportable The non-reportable segments include five operating segments that consist of support services provided to the Company's customers and independent contractors (including repair and maintenance shop services, equipment leasing, warranty services, and insurance), trailer parts manufacturing, warehousing, and certain driving academy activities, as well as certain corporate expenses (such as legal settlements and accruals, certain impairments, and amortization of intangibles related to the 2017 Merger and various acquisitions). Intersegment Eliminations Certain operating segments provide transportation and related services for other affiliates outside of their segments. For certain operating segments, such services are billed at cost, and no profit is earned. For the other operating segments, revenues for such services are based on negotiated rates, and are reflected as revenues of the billing segment. These rates are adjusted from time to time, based on market conditions. Such intersegment revenues and expenses are eliminated in Knight-Swift's consolidated results. The following tables present the Company's financial information by segment: Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 Revenue: (In thousands) Truckload $ 1,041,332 $ 975,881 $ 2,990,137 $ 2,774,311 Logistics 226,338 99,018 511,962 248,320 Intermodal 112,801 98,859 335,245 276,410 LTL 191,906 — 191,906 — Subtotal $ 1,572,377 $ 1,173,758 $ 4,029,250 $ 3,299,041 Non-reportable segments 89,393 56,610 206,857 148,141 Intersegment eliminations (19,325) (19,962) (54,947) (51,280) Total revenue $ 1,642,445 $ 1,210,406 $ 4,181,160 $ 3,395,902 Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 Operating income (loss): (In thousands) Truckload $ 206,543 $ 168,781 $ 533,483 $ 383,903 Logistics 27,128 2,478 49,061 9,235 Intermodal 9,544 250 18,813 (6,962) LTL 17,469 $ — 17,469 $ — Subtotal $ 260,684 $ 171,509 $ 618,826 $ 386,176 Non-reportable segments 9,403 (6,048) 4,635 (16,429) Operating income $ 270,087 $ 165,461 $ 623,461 $ 369,747 Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 Depreciation and amortization of property and equipment: (In thousands) Truckload $ 107,229 $ 97,867 $ 314,320 $ 288,970 Logistics 355 214 852 628 Intermodal 3,942 3,564 11,700 10,658 LTL 11,950 $ — 11,950 $ — Subtotal $ 123,476 $ 101,645 $ 338,822 $ 300,256 Non-reportable segments 15,094 14,019 43,269 40,230 Depreciation and amortization of property and equipment $ 138,570 $ 115,664 $ 382,091 $ 340,486 Geographical Information In the aggregate, total revenue from the Company's international operations was less than 5.0% of consolidated total revenue for the quarter and year-to-date periods ended September 30, 2021 and 2020. Additionally, long-lived assets on the Company's international subsidiary balance sheets were less than 5.0% of consolidated total assets as of September 30, 2021 and December 31, 2020.

Introduction and Basis of Pre_2

Introduction and Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	In management's opinion, these condensed consolidated financial statements were prepared in accordance with GAAP and include all adjustments necessary (consisting of normal recurring adjustments) for the fair statement of the periods presented.

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Business Acquisition, Pro Forma Information	The following unaudited pro forma information combines the historical operations of the Company and ACT giving effect to the ACT Acquisition, and related transactions as if consummated on January 1, 2020, the beginning of the comparative period presented. Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 (in thousands, except per share data) (in thousands, except per share data) Total revenue $ 1,642,445 $ 1,388,490 $ 4,570,470 $ 3,911,986 Net income attributable to Knight-Swift 202,883 129,295 507,168 284,095 Earnings per share – diluted 1.21 0.76 3.04 1.66
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	ACT UTXL Eleos July 5, 2021 Opening Balance Sheet as Reported at September 30, 2021 June 1, 2021 Opening Balance Sheet as Reported at September 30, 2021 February 1, 2021 Opening Balance Sheet as Reported at September 30, 2021 Fair value of the consideration transferred $ 1,306,214 $ 37,230 $ 41,518 Cash and cash equivalents 17,477 8,206 2,237 Trade receivables 104,220 9,451 545 Prepaid expenses 15,803 — 47 Other current assets 3,537 — — Property and equipment 427,722 54 — Operating lease right-of-use assets 4,053 — 560 Identifiable intangible assets 1 406,160 22,121 15,850 Other noncurrent assets 1,739 — — Total assets 980,711 39,832 19,239 Accounts payable (19,386) (14,183) (156) Accrued payroll and payroll-related expenses (33,411) (247) (605) Accrued liabilities (9,302) (69) (1,391) Claims accruals – current and noncurrent portions (40,958) (418) — Operating lease liabilities – current and noncurrent portions (4,052) — (560) Long-term debt – current and noncurrent portions (54,024) — — Other long-term liabilities (4,243) — (475) Total liabilities (165,376) (14,917) (3,187) Noncontrolling interest — — (10,281) Total stockholders' equity — — (10,281) Goodwill $ 490,879 $ 12,315 $ 35,747 1 Includes $278.8 million in customer relationships, $1.2 million in noncompete agreements, $10.0 million in internally developed software, and $154.1 million in trade names.

Restricted Investments, Held-to

Restricted Investments, Held-to-Maturity (Tables)	9 Months Ended
	Sep. 30, 2021
Schedule of Investments [Abstract]
Schedule of Restricted Investments, Held-to-Maturity	The following tables present the cost or amortized cost, gross unrealized gains and temporary losses, and estimated fair value of the Company's restricted investments, held-to-maturity: September 30, 2021 Gross Unrealized Cost or Amortized Gains Temporary Estimated Fair Value (In thousands) US corporate securities $ 7,140 $ — $ (6) $ 7,134 Restricted investments, held-to-maturity $ 7,140 $ — $ (6) $ 7,134 December 31, 2020 Gross Unrealized Cost or Amortized Gains Temporary Estimated Fair Value (In thousands) US corporate securities $ 9,001 $ 2 $ (8) $ 8,995 Restricted investments, held-to-maturity $ 9,001 $ 2 $ (8) $ 8,995

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The changes in the carrying amount of goodwill were as follows: (In thousands) Goodwill, balance at December 31, 2020 $ 2,922,964 Adjustments relating to deferred tax assets (7) Acquisitions 1 538,941 Goodwill, balance at September 30, 2021 $ 3,461,898
Schedule of Intangible Assets, net	Other intangible asset balances were as follows: September 30, 2021 December 31, (In thousands) Definite-lived intangible assets 1 Gross carrying amount $ 1,187,970 $ 894,597 Accumulated amortization (185,304) (145,852) Definite-lived intangible assets, net 1,002,666 748,745 Indefinite-lived trade names: Gross carrying amount 791,258 640,500 Intangible assets, net $ 1,793,924 $ 1,389,245

Accounts Receivable Securitiz_2

Accounts Receivable Securitization (Tables)	9 Months Ended
	Sep. 30, 2021
Transfers and Servicing [Abstract]
Schedule of Servicing Liabilities at Fair Value [Table Text Block]	The following table summarizes the key terms of the 2021 RSA and 2018 RSA (dollars in thousands): 2021 RSA 2018 RSA Effective date April 23, 2021 July 11, 2018 Final maturity date April 23, 2024 July 9, 2021 Borrowing capacity $400,000 $325,000 Accordion option 1 $100,000 $175,000 Unused commitment fee rate 2 20 to 40 basis points 20 to 40 basis points Program fees on outstanding balances 3 4 one-month LIBOR + 82.5 basis points one-month LIBOR + 80 to 100 basis points 1 The accordion option increases the maximum borrowing capacity, subject to participation of the purchasers. 2 The 2021 RSA and 2018 RSA commitment fees rate are based on the percentage of the maximum borrowing capacity utilized. 3 Only the rate for the 2018 RSA program fee is subject to the Company's consolidated total net leverage ratio. 4 As identified within the 2021 RSA, the lender can trigger an amendment by identifying and deciding upon a replacement for LIBOR. Availability under the 2021 RSA and 2018 RSA is calculated as follows: 2021 RSA 2018 RSA September 30, 2021 December 31, 2020 (In thousands) Borrowing base, based on eligible receivables $ 400,000 $ 302,700 Less: outstanding borrowings 1 (279,000) (214,000) Less: outstanding letters of credit, net (65,300) (67,281) Availability under accounts receivable securitization facilities $ 55,700 $ 21,419 1 As of September 30, 2021, outstanding borrowings are included in "Accounts receivable securitization – less current portion" in the condensed consolidated balance sheets and are offset by $0.6 million of deferred loan costs. As of December 31, 2020, outstanding borrowings are included in "Accounts receivable securitization – current portion" in the condensed consolidated balance sheets and are offset by $0.1 million of deferred loan costs . Interest accrued on the aggregate principal balance at a rate of 0.9% and 1.0% as of September 30, 2021 and December 31, 2020, respectively.

Debt And Financing (Tables)

Debt And Financing (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Debt Balances by Instrument	Other than the Company's accounts receivable securitization as discussed in Note 8, the Company's long-term debt consisted of the following: September 30, 2021 December 31, 2020 (In thousands) 2021 Term Loan A-1, due December 3, 2022, net 1 2 $ 199,588 $ — 2021 Term Loan A-2, due September 3, 2024, net 1 2 199,571 — 2021 Term Loan A-3, due September 3, 2026, net 1 2 798,264 — 2017 Term Loan, due October 2022, net 1 3 — 298,907 2021 Prudential Notes, net 47,760 — Other 5,567 — Total long-term debt, including current portion 1,250,750 298,907 Less: current portion of long-term debt (12,728) — Long-term debt, less current portion $ 1,238,022 $ 298,907 September 30, 2021 December 31, 2020 (In thousands) Total long-term debt, including current portion $ 1,250,750 $ 298,907 2021 Revolver, due September 3, 2026 1 4 300,000 — 2017 Revolver, due October 2022 1 5 — 210,000 Long-term debt, including revolving line of credit $ 1,550,750 $ 508,907 1 Refer to Note 15 for information regarding the fair value of debt. 2 The carrying amounts of the 2021 Term Loan A-1, 2021 Term Loan A-2, and 2021 Term Loan A-3 are net of $0.4 million, $0.4 million, and $1.7 million in deferred loan costs as of September 30, 2021, respectively. 3 Net of $1.1 million deferred loan costs at December 31, 2020. 4 The Company also had outstanding letters of credit of $63.8 million under the 2021 Revolver, primarily related to workers' compensation and self-insurance liabilities at September 30, 2021. Subsequent to September 30, 2021, we paid $95.0 million on the 2021 Revolver. 5 The Company also had outstanding letters of credit of $29.3 million under the 2017 Revolver, primarily related to workers' compensation and self-insurance liabilities at December 31, 2020.
Schedule of Long-term Debt Instruments	The following table presents the key terms of the 2021 Debt Agreement: 2021 Term Loan A-1 2021 Term Loan A-2 2021 Term Loan A-3 2021 Revolver 2 2021 Debt Agreement Terms (Dollars in thousands) Maximum borrowing capacity $200,000 $200,000 $800,000 $1,100,000 Final maturity date December 3, 2022 September 3, 2024 September 3, 2026 September 3, 2026 Interest rate minimum margin BSBY BSBY BSBY BSBY Interest rate minimum margin 1 0.75% 0.75% 0.88% 0.88% Interest rate maximum margin 1 1.38% 1.38% 1.50% 1.50% Minimum principal payment — amount $— $— $10,000 $— Minimum principal payment — frequency Once Once Quarterly Once Minimum principal payment — commencement date December 3, 2022 September 3, 2024 September 30, 2024 September 3, 2026 1 The interest rate margin for the 2021 Term Loans and 2021 Revolver is based on the Company's consolidated leverage ratio. As of September 30, 2021, interest accrued at 1.1% on the 2021 Term Loans and 1.2% on the 2021 Revolver. 2 The commitment fee for the unused portion of the 2021 Revolver is based on the Company's consolidated leverage ratio, and ranges from 0.1% to 0.2%. As of September 30, 2021, commitment fees on the unused portion of the 2021 Revolver accrued at 0.1% and outstanding letter of credit fees accrued at 1.1%.

Defined Benefit Pension Plan (T

Defined Benefit Pension Plan (Tables)	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Schedule of Amounts Recognized in Balance Sheet	The net pension liability recognized is as follows: September 30, 2021 (In thousands) Projected benefit obligation $ 71,263 Less: fair value of plan assets 69,400 Unfunded status 1,863 Accrued pension liability recognized 1 $ 1,863
Schedule of Defined Benefit Plans Disclosures	Other information concerning the defined benefit pension plan is summarized below: Quarter-to-Date September 30, 2021 (In thousands) Net periodic pension income $ 596 Benefits paid 771 The following benefit payments are expected to be paid in each of the fiscal years as follows: September 30, 2021 (In thousands) Remainder of 2021 $ 874 2022 3,593 2023 3,707 2024 3,851 2025 3,953 2026 4,040 2027 through 2030 16,453 Total $ 36,471
Defined Benefit Plan, Assumptions	The following weighted-average assumptions were used to determine net periodic pension cost: Quarter-to-Date September 30, 2021 Discount rate 2.49 % Expected long-term rate of return on pension plan assets 6.00 %
Defined Benefit Plan, Plan Assets, Allocation	The defined benefit pension plan weighted-average asset allocations, by asset category, are as follows: September 30, 2021 Asset category: Equity securities 30 % Debt securities 69 % Cash and cash equivalents 1 % Total 100 % The target allocation by asset category, is as follows: September 30, 2021 Asset category: Equity securities 30 % Debt securities 70 % Total 100 %

Contingencies and Legal Proce_2

Contingencies and Legal Proceedings (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Schedule of Loss Contingencies by Contingency	EMPLOYEE COMPENSATION AND PAY PRACTICES MATTERS CRST Expedited The plaintiff alleges tortious interference with contract and unjust enrichment related to non-competition agreements entered into with certain of its drivers. Plaintiff(s) Defendant(s) Date instituted Court or agency currently pending in CRST Expedited, Inc. Swift Transportation Co. of Arizona LLC. March 20, 2017 United States District Court for the Northern District of Iowa Recent Developments and Current Status In July 2019, a jury issued an adverse verdict in this lawsuit. The court issued a decision granting in part and denying in part certain motions related to the jury’s verdict. Both parties have appealed the court’s decision. On August 6, 2021 a three-judge panel of the 8th Circuit Court of Appeals issued an opinion reversing the trial court’s decision. On October 4, 2021 the 8th Circuit Court of Appeals denied a petition for rehearing. The likelihood that a loss has been incurred is no longer probable, and the accrual for this lawsuit has accordingly been reversed as of September 30, 2021. California Wage, Meal, and Rest Class Actions The plaintiffs generally allege one or more of the following: that the Company 1) failed to pay the California minimum wage; 2) failed to provide proper meal and rest periods; 3) failed to timely pay wages upon separation from employment; 4) failed to pay for all hours worked; 5) failed to pay overtime; 6) failed to properly reimburse work-related expenses; and 7) failed to provide accurate wage statements. Plaintiff(s) Defendant(s) Date instituted Court or agency currently pending in John Burnell 1 Swift Transportation Co., Inc March 22, 2010 United States District Court for the Central District of California James R. Rudsell 1 Swift Transportation Co. of Arizona, LLC and Swift Transportation Company April 5, 2012 United States District Court for the Central District of California Recent Developments and Current Status In April 2019, the parties reached settlement of this matter. In January 2020, the court granted final approval of the settlement. Two objectors appealed the court’s decision granting final approval of the settlement. The likelihood that a loss has been incurred is probable and estimable, and the loss has accordingly been accrued as of September 30, 2021. INDEPENDENT CONTRACTOR MATTERS Ninth Circuit Independent Contractor Misclassification Class Action The putative class alleges that Swift misclassified independent contractors as independent contractors, instead of employees, in violation of the Fair Labor Standards Act and various state laws. The lawsuit also raises certain related issues with respect to the lease agreements that certain independent contractors have entered into with Interstate Equipment Leasing, LLC. The putative class seeks unpaid wages, liquidated damages, interest, other costs, and attorneys' fees. Plaintiff(s) Defendant(s) Date instituted Court or agency currently pending in Joseph Sheer, Virginia Van Dusen, Jose Motolinia, Vickii Schwalm, Peter Wood 1 Swift Transportation Co., Inc., Interstate Equipment Leasing, Inc., Jerry Moyes, and Chad Killebrew December 22, 2009 Unites States District Court of Arizona and Ninth Circuit Court of Appeals Recent Developments and Current Status In January 2020, the court granted final approval of the settlement in this matter. In March 2020, the Company paid the settlement amount approved by the court. As of September 30, 2021, the Company has accrued for anticipated costs associated with finalizing this matter. 1 Individually and on behalf of all others similarly situated.

Share Repurchase Plans (Tables)

Share Repurchase Plans (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Schedule of Share Repurchases	The following table presents the Company's repurchases of its common stock under the respective share repurchase plans, excluding advisory fees: Share Repurchase Plan Quarter-to-Date September 30, 2021 Year-to-Date September 30, 2021 Board Approval Date Authorized Amount Shares Amount Shares Amount (shares and dollars in thousands) November 24, 2020 1 $250,000 — $ — 1,303 $ 53,661 Quarter-to-Date September 30, 2020 Year-to-Date September 30, 2020 May 30, 2019 $250,000 — $ — 1,139 $ 34,630 1 $196.3 million and $250.0 million remained available under the 2020 Knight-Swift Share Repurchase Plan as of September 30, 2021 and December 31, 2020, respectively.

Weighted Average Shares Outst_2

Weighted Average Shares Outstanding (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Calculation Of Basic And Diluted Earnings Per Share Attributable To Stockholders	The following table reconciles basic weighted average shares outstanding to diluted weighted average shares outstanding: Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 (In thousands) Basic weighted average common shares outstanding 165,966 170,205 165,823 170,257 Dilutive effect of equity awards 1,140 823 1,113 778 Diluted weighted average common shares outstanding 167,106 171,028 166,936 171,035 Anti-dilutive shares excluded from diluted earnings per share 1 23 8 165 187 1 Shares were excluded from the dilutive-effect calculation because the outstanding awards' exercise prices were greater than the average market price of the Company's common stock for the periods presented.

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value by Balance Sheet Grouping	The following table presents the carrying amounts and estimated fair values of the Company's major categories of financial assets and liabilities: September 30, 2021 December 31, 2020 Condensed Consolidated Balance Sheets Caption Carrying Estimated Carrying Estimated (In thousands) Financial Assets: Restricted investments, held-to-maturity 1 Restricted investments, held-to-maturity, amortized cost $ 7,140 $ 7,134 $ 9,001 $ 8,995 Equity method investments Other long-term assets 82,883 82,883 77,562 77,562 Investments in equity securities Other long-term assets 21,063 21,063 18,675 18,675 Convertible note Other current assets 37,631 37,631 — — Financial Liabilities: 2017 Term Loan, due October 2022 2 Long-term debt – less current portion $ — $ — $ 298,907 $ 300,000 2021 Term Loan A-1, due December 2022 3 Long-term debt – less current portion 199,588 200,000 — — 2021 Term Loan A-2, due September, 2024 3 Long-term debt – less current portion 199,571 200,000 — — 2021 Term Loan A-3, due September 2026 3 Long-term debt – less current portion 798,264 800,000 — — 2018 RSA, due July 2021 4 Accounts receivable securitization — — 213,918 214,000 2021 RSA, due April 2024 5 Accounts receivable securitization 278,428 279,000 — — 2017 Revolver, due October 2022 Revolving line of credit — — 210,000 210,000 2021 Revolver, due September 2026 Revolving line of credit 300,000 300,000 — — 2021 Prudential Notes 6 Finance lease liabilities and long-term debt 47,760 50,321 — — Contingent consideration, acquisitions Accrued liabilities, Other long-term liabilities 21,200 21,200 16,200 16,200 1 Refer to Note 4 for the differences between the carrying amounts and estimated fair values of the Company's restricted investments, held-to-maturity. 2 The carrying amount of the 2017 Term Loan is net of $1.1 million in deferred loan costs as of December 31, 2020. 3 The carrying amounts of the 2021 Term Loan A-1, 2021 Term Loan A-2, and 2021 Term Loan A-3 are net of $0.4 million, $0.4 million, and $1.7 million in deferred loan costs as of September 30, 2021, respectively. 4 The carrying amount of the 2018 RSA is net of $0.1 million in deferred loan costs as of December 31, 2020 . 5 The carrying amount of the 2021 RSA is net of $0.6 million in deferred loan costs as of September 30, 2021 . 6 The carrying amount of the 2021 Prudential Notes is net of $0.1 million in deferred loan costs and $2.4 million in fair value adjustments as of September 30, 2021 .
Recurring Fair Value Measurements (Assets)	The following table depicts the level in the fair value hierarchy of the inputs used to estimate the fair value of assets measured on a recurring basis as of September 30, 2021 and December 31, 2020 : Fair Value Measurements at Reporting Date Using: Estimated Level 1 Inputs Level 2 Inputs Level 3 Inputs Unrealized Gain Position (In thousands) As of September 30, 2021 Convertible note 1 $ 37,631 $ — $ — $ 37,631 $ 12,631 Investments in equity securities 2 $ 21,063 $ 21,063 $ — $ — $ 11,135 As of December 31, 2020 Investments in equity securities 3 $ 18,675 $ 18,675 $ — $ — $ 3,553 1 The Company recognized $12.6 million of unrealized gains on the convertible note for the year-to-date period ended September 30, 2021, which is included within "Other income, net" within the condensed consolidated statement of comprehensive income. The fair value of the note was determined using a discounted cash flow analysis based on the probability of exit event options and exit event dates. 2 Fair value activity from the investments in equity securities is recorded in "Other income, net" within the condensed consolidated statement of comprehensive income. • During the quarter ended September 30, 2021, the Company recognized $4.0 million in gains on these investments in equity securities, consisting of $3.0 million in unrealized gains and $1.0 million in realized gains. • During the year-to-date period ended September 30, 2021, the Company recognized $12.8 million in gains on these investments in equity securities, consisting of $7.6 million in unrealized gains and $5.2 million in realized gains. 3 Fair value activity from the investments in equity securities is recorded in "Other income, net" within the condensed consolidated statement of comprehensive income. • During the quarter ended September 30, 2020, the Company recognized $4.4 million in unrealized gains on these investments in equity securities. • During the year-to-date period ended September 30, 2020, the Company recognized $6.9 million in unrealized gains on these investments in equity securities. Fair Value Measurements at Reporting Date Using: Estimated Level 1 Inputs Level 2 Inputs Level 3 Inputs (In thousands) As of September 30, 2021 US equity funds $ 14,810 $ 14,810 $ — $ — International equity funds 6,184 6,184 — — Fixed income funds 47,583 47,583 — — Cash and cash equivalents 823 823 — — Total pension plan assets $ 69,400 $ 69,400 $ — $ —
Recurring Fair Value Measurements (Liabilities)	The following table depicts the level in the fair value hierarchy of the inputs used to estimate the fair value of liabilities measured on a recurring basis as of September 30, 2021 and December 31, 2020: Fair Value Measurements at Reporting Date Using: Estimated Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Gain (Loss) (In thousands) As of September 30, 2021 Contingent consideration associated with acquisitions 1 $ 21,200 $ — $ — $ 21,200 $ — As of December 31, 2020 Contingent consideration associated with acquisition 2 $ 16,200 $ — $ — $ 16,200 $ (6,730) 1 The Company did not recognize any gains (losses) during the quarter or year-to-date periods ended September 30, 2021 related to the revaluation of these liabilities. Refer to Note 3 for information regarding the components of these liabilities. 2 During the fourth quarter of 2020, the Company increased the estimated fair value of the remaining contingent consideration representing the final two annual payments, resulting in a $6.7 million fair value adjustment of the deferred earnout, which was recorded in “Miscellaneous operating expenses” in the consolidated statement of comprehensive income. The Company did not recognize any losses during the quarter and year-to-date periods ended September 30, 2020.
Nonrecurring Fair Value Measurements (Assets)	The following table depicts the level in the fair value hierarchy of the inputs used to estimate fair value of assets measured on a nonrecurring basis as of December 31, 2020: Fair Value Measurements at Reporting Date Using: Estimated Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Loss (In thousands) As of December 31, 2020 Equipment 1 5,851 — 5,851 — (5,335)

Related Party Transactions (Tab

Related Party Transactions (Tables)	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	The following table presents Knight-Swift's transactions with companies controlled by and/or affiliated with its related parties: Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 Provided by Knight-Swift Received by Knight-Swift Provided by Knight-Swift Received by Knight-Swift Provided by Knight-Swift Received by Knight-Swift Provided by Knight-Swift Received by Knight-Swift (In thousands) Freight Services: Central Freight Lines 1 $ — $ — $ 1 $ — $ — $ — $ 7,837 $ — SME Industries 1 — — 28 — — — 56 — Total $ — $ — $ 29 $ — $ — $ — $ 7,893 $ — Facility and Equipment Leases: Central Freight Lines 1 $ — $ — $ 25 $ 92 $ — $ — $ 48 $ 277 Other Affiliates 1 — 69 2 37 — 214 11 146 Total $ — $ 69 $ 27 $ 129 $ — $ 214 $ 59 $ 423 Other Services: Central Freight Lines 1 $ — $ — $ 412 $ — $ — $ — $ 427 $ — DPF Mobile 1 — — — 2 — — — 33 Other Affiliates 1 8 9 13 — 21 27 32 — Total $ 8 $ 9 $ 425 $ 2 $ 21 $ 27 $ 459 $ 33 1 Entities affiliated with former Board member Jerry Moyes include Central Freight Lines, SME Industries, and DPF Mobile. "Other affiliates" includes entities that are associated with various board members and executives and require approval by the Board prior to completing transactions. Transactions with these entities generally include freight services, facility and equipment leases, equipment sales, and other services. • Freight Services Provided by Knight-Swift — The Company charges each of these companies for transportation services. • Freight Services Received by Knight-Swift — Transportation services received from Central Freight Lines represent less-than-truckload freight services rendered to haul parts and equipment to Company shop locations. • Other Services Provided by Knight-Swift — Other services provided by the Company to the identified related parties include equipment sales and miscellaneous services. • Other Services Received by Knight-Swift — Consulting fees, diesel particulate filter cleaning, sales of various parts and tractor accessories, and certain third-party payroll and employee benefits administration services from the identified related parties are included in other services received by the Company. During the quarter ended September 30, 2020, the ownership percentage of Jerry Moyes and related affiliates fell below the threshold requiring related party disclosure. The amounts included in this Note 16 pertain to transactions that occurred prior to the date that the ownership percentage changed. Receivables and payables pertaining to related party transactions were: September 30, 2021 December 31, 2020 Receivable Payable Receivable Payable (In thousands) Central Freight Lines $ — $ — $ 133 $ — DPF Mobile — — — 41 Other Affiliates 6 44 2 10 Total $ 6 $ 44 $ 135 $ 51

Information by Segment and Ge_2

Information by Segment and Geography (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Summary Of Financial Information By Segments	The following tables present the Company's financial information by segment: Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 Revenue: (In thousands) Truckload $ 1,041,332 $ 975,881 $ 2,990,137 $ 2,774,311 Logistics 226,338 99,018 511,962 248,320 Intermodal 112,801 98,859 335,245 276,410 LTL 191,906 — 191,906 — Subtotal $ 1,572,377 $ 1,173,758 $ 4,029,250 $ 3,299,041 Non-reportable segments 89,393 56,610 206,857 148,141 Intersegment eliminations (19,325) (19,962) (54,947) (51,280) Total revenue $ 1,642,445 $ 1,210,406 $ 4,181,160 $ 3,395,902 Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 Operating income (loss): (In thousands) Truckload $ 206,543 $ 168,781 $ 533,483 $ 383,903 Logistics 27,128 2,478 49,061 9,235 Intermodal 9,544 250 18,813 (6,962) LTL 17,469 $ — 17,469 $ — Subtotal $ 260,684 $ 171,509 $ 618,826 $ 386,176 Non-reportable segments 9,403 (6,048) 4,635 (16,429) Operating income $ 270,087 $ 165,461 $ 623,461 $ 369,747 Quarter-to-Date September 30, Year-to-Date September 30, 2021 2020 2021 2020 Depreciation and amortization of property and equipment: (In thousands) Truckload $ 107,229 $ 97,867 $ 314,320 $ 288,970 Logistics 355 214 852 628 Intermodal 3,942 3,564 11,700 10,658 LTL 11,950 $ — 11,950 $ — Subtotal $ 123,476 $ 101,645 $ 338,822 $ 300,256 Non-reportable segments 15,094 14,019 43,269 40,230 Depreciation and amortization of property and equipment $ 138,570 $ 115,664 $ 382,091 $ 340,486

Introduction and Description of

Introduction and Description of Business (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)Vehicle	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)VehicleSegment	Sep. 30, 2020USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operational tractors in fleet	18,041		18,041
Number of company tractors	16,166		16,166
Number of independent contractor tractors	1,875		1,875
Number of trailers	60,396		60,396
Number of intermodal tractors	605		605
Number of intermodal containers	10,843		10,843
Number of reportable segments | Segment			4
Change in Accounting Estimate [Line Items]
Depreciation and amortization of property and equipment | $	$ 138,570	$ 115,664	$ 382,091	$ 340,486
Service Life
Change in Accounting Estimate [Line Items]
Change in Accounting Estimate, Description			In September 2021, the Company increased the useful life for a certain group of its trailers, given recent trends in the used trailer market. Management prospectively accounted for this as a change in accounting estimate.
Depreciation and amortization of property and equipment | $	$ 600		$ 600

Acquisitions - Narrative (Detai

Acquisitions - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jul. 05, 2021	Jun. 01, 2021	Feb. 01, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Total revenue					$ 1,642,445	$ 1,210,406	$ 4,181,160	$ 3,395,902
Net income					206,166	122,204	489,144	268,254
Amortization of Intangible Assets					15,719	$ 11,473	39,452	$ 34,421
Business Combination, Contingent Consideration, Liability	$ 21,200				21,200		21,200		$ 16,200
ACT
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Jul. 5, 2021
Business Acquisition, Percentage of Voting Interests Acquired		100.00%
Fair value of the consideration transferred	1,306,214	$ 1,310,000
Business Combination, Consideration Transferred, Liabilities Incurred		36,500
Total revenue					191,900		191,900
Net income					13,400		13,400
Amortization of Intangible Assets					3,500		3,500
Business Combination, Acquisition Related Costs					2,400		2,700
UTXL [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition			Jun. 1, 2021
Business Acquisition, Percentage of Voting Interests Acquired			100.00%
Fair value of the consideration transferred	37,230		$ 37,200
Eleos [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition				Feb. 1, 2021
Business Acquisition, Percentage of Voting Interests Acquired				79.44%
Fair value of the consideration transferred	41,518			$ 41,500
Warehousing Co [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability	16,200				16,200		16,200		$ 16,200
Cash paid for acquisition [Member] | ACT
Business Acquisition [Line Items]
Fair value of the consideration transferred		1,300,000
Cash paid for acquisition [Member] | UTXL [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred			32,200
Escrow For Sellers Indemnification Obligations [Member] | UTXL [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred			2,250
Escrow For Sellers Indemnification Obligations [Member] | Eleos [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred				$ 4,100
Contingent consideration (total payment) [Member] | UTXL [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability			5,000
Contingent consideration (annual payment) [Member] | UTXL [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability, Current	2,500		$ 2,500		2,500		2,500
Business Combination, Contingent Consideration, Liability, Noncurrent	$ 2,500				$ 2,500		$ 2,500
Equity transferred in acquisition | ACT
Business Acquisition [Line Items]
Fair value of the consideration transferred		$ 10,000

Acquisitions - Tables (Details)

Acquisitions - Tables (Details) - USD ($) $ / shares in Units, $ in Thousands		Sep. 30, 2021	Jul. 05, 2021	Jun. 01, 2021	Feb. 01, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Revenue						$ 1,642,445	$ 1,388,490	$ 4,570,470	$ 3,911,986
Business Acquisition, Pro Forma Net Income (Loss)						$ 202,883	$ 129,295	$ 507,168	$ 284,095
Business Acquisition, Pro Forma Earnings Per Share, Diluted						$ 1.21	$ 0.76	$ 3.04	$ 1.66
Noncontrolling interest								$ (10,281)
Goodwill		$ 3,461,898				$ 3,461,898		3,461,898		$ 2,922,964
Trade Names		154,100				154,100		154,100
Customer relationships [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets		278,800				278,800		278,800
Noncompete agreements [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets		1,200				1,200		1,200
Internally developed software [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets		10,000				10,000		10,000
ACT
Business Acquisition [Line Items]
Fair value of the consideration transferred		1,306,214	$ 1,310,000
Cash and cash equivalents		17,477				17,477		17,477
Trade receivables		104,220				104,220		104,220
Prepaid expenses		15,803				15,803		15,803
Other current assets		3,537				3,537		3,537
Property and equipment		427,722				427,722		427,722
Operating lease right-of-use assets		4,053				4,053		4,053
Identifiable intangible assets 1	[1]	406,160				406,160		406,160
Other noncurrent assets		1,739				1,739		1,739
Total assets		980,711				980,711		980,711
Accounts payable		(19,386)				(19,386)		(19,386)
Accrued payroll and payroll-related expenses		(33,411)				(33,411)		(33,411)
Accrued liabilities		(9,302)				(9,302)		(9,302)
Claims accruals – current and noncurrent portions		(40,958)				(40,958)		(40,958)
Operating lease liabilities – current and noncurrent portions		(4,052)				(4,052)		(4,052)
Long-term debt – current and noncurrent portions		(54,024)				(54,024)		(54,024)
Other long-term liabilities		(4,243)				(4,243)		(4,243)
Total liabilities		(165,376)				(165,376)		(165,376)
Noncontrolling interest		0
Total stockholders' equity		0				0		0
Goodwill		490,879				490,879		490,879
UTXL [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred		37,230		$ 37,200
Cash and cash equivalents		8,206				8,206		8,206
Trade receivables		9,451				9,451		9,451
Prepaid expenses		0				0		0
Other current assets		0				0		0
Property and equipment		54				54		54
Operating lease right-of-use assets		0				0		0
Identifiable intangible assets 1	[1]	22,121				22,121		22,121
Other noncurrent assets		0				0		0
Total assets		39,832				39,832		39,832
Accounts payable		(14,183)				(14,183)		(14,183)
Accrued payroll and payroll-related expenses		(247)				(247)		(247)
Accrued liabilities		(69)				(69)		(69)
Claims accruals – current and noncurrent portions		(418)				(418)		(418)
Operating lease liabilities – current and noncurrent portions		0				0		0
Long-term debt – current and noncurrent portions		0				0		0
Other long-term liabilities		0				0		0
Total liabilities		(14,917)				(14,917)		(14,917)
Noncontrolling interest		0
Total stockholders' equity		0				0		0
Goodwill		12,315				12,315		12,315
Eleos [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred		41,518			$ 41,500
Cash and cash equivalents		2,237				2,237		2,237
Trade receivables		545				545		545
Prepaid expenses		47				47		47
Other current assets		0				0		0
Property and equipment		0				0		0
Operating lease right-of-use assets		560				560		560
Identifiable intangible assets 1	[1]	15,850				15,850		15,850
Other noncurrent assets		0				0		0
Total assets		19,239				19,239		19,239
Accounts payable		(156)				(156)		(156)
Accrued payroll and payroll-related expenses		(605)				(605)		(605)
Accrued liabilities		(1,391)				(1,391)		(1,391)
Claims accruals – current and noncurrent portions		0				0		0
Operating lease liabilities – current and noncurrent portions		(560)				(560)		(560)
Long-term debt – current and noncurrent portions		0				0		0
Other long-term liabilities		(475)				(475)		(475)
Total liabilities		(3,187)				(3,187)		(3,187)
Noncontrolling interest		(10,281)
Total stockholders' equity		(10,281)				(10,281)		(10,281)
Goodwill		$ 35,747				$ 35,747		$ 35,747
[1]	Includes $278.8 million in customer relationships, $1.2 million in noncompete agreements, $10.0 million in internally developed software, and $154.1 million in trade names.

Restricted Investments, Held-_2

Restricted Investments, Held-to-Maturity (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021USD ($)Securities	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)Securities	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)Securities
Schedule of Investments [Line Items]
Cost or Amortized Cost	[1]	$ 7,140		$ 7,140		$ 9,001
Gross Unrealized Gains		0		0		2
Gross Unrealized Temporary Losses		(6)		(6)		(8)
Restricted investments, held-to-maturity 1	[1]	$ 7,134		$ 7,134		$ 8,995
Securities with unrealized losses for less than 12 months | Securities		13		13		16
Impairment losses		$ 0	$ 0	$ 0	$ 0
US corporate securities [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost		7,140		7,140		$ 9,001
Gross Unrealized Gains		0		0		2
Gross Unrealized Temporary Losses		(6)		(6)		(8)
Restricted investments, held-to-maturity 1		$ 7,134		$ 7,134		$ 8,995
Maximum [Member]
Schedule of Investments [Line Items]
Contractual maturities of fixed maturity securities				1 year
Duration of securities in unrealized loss position				12 months
[1]	Refer to Note 4 for the differences between the carrying amounts and estimated fair values of the Company's restricted investments, held-to-maturity.

Embark Convertible Note (Detail

Embark Convertible Note (Details) - USD ($) $ in Thousands	Apr. 16, 2021	Sep. 30, 2021	Dec. 31, 2020
Schedule of Investments [Abstract]
Investment Owned, Face Amount	$ 25,000
Convertible Note Interest Rate	10.00%
Investment Owned, at Fair Value		$ 37,631	$ 0

Assets Held For Sale (Details)

Assets Held For Sale (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Long Lived Assets Held-for-sale [Line Items]
Period Assets are Expected To Be Sold			12 months
Gain on disposal of assets held for sale			$ 47,700	$ 6,468
Equipment [Member]
Long Lived Assets Held-for-sale [Line Items]
Assets Held for Sale		$ 16,700		16,700	$ 29,800
Gain on disposal of assets held for sale	$ 22,100	1,700	47,700	6,500
Impairments	$ 0	400	$ 0	400
Land and Land Improvements
Long Lived Assets Held-for-sale [Line Items]
Assets Held for Sale		$ 3,600		$ 3,600	$ 0

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets Summary of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill		$ 3,461,898		$ 3,461,898		$ 2,922,964
Adjustments relating to deferred tax assets				(7)
Acquisition	[1]			538,941
Goodwill impairments		$ 0	$ 0	$ 0	$ 0
[1]	The goodwill associated with the ACT, UTXL and Eleos acquisitions referenced in Note 3 was allocated to the LTL, Logistics, and non-reportable segments, respectively, and is net of purchase price accounting adjustments.

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets Intangible Asset Balances (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2021	Dec. 31, 2020
Definite-lived intangible assets 1
Gross carrying amount	[1]	$ 1,187,970	$ 894,597
Accumulated amortization		(185,304)	(145,852)
Definite-lived intangible assets, net		1,002,666	748,745
Indefinite-lived trade names:
Gross carrying amount		791,258	640,500
Intangible assets, net		$ 1,793,924	$ 1,389,245
Intangible Assets Other Than the 2017 Merger [Member]
Schedule of finite-lived intangible assets amortization expense [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		18 years 10 months 24 days
Intangible assets related to the 2017 Merger [Member] [Member]
Schedule of finite-lived intangible assets amortization expense [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		19 years 10 months 24 days
[1]	The major categories of the Company's definite-lived intangible assets include customer relationships, non-compete agreements, internally-developed software, trade names, and others.

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets Narrative (Details) $ in Millions	Sep. 30, 2021USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense, 2021	$ 15.9
Amortization expense, 2022	62.8
Amortization expense, 2023	62.2
Amortization expense, 2024	62.2
Amortization Expense, 2025	$ 62.1

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Income Tax Contingency [Line Items]
Effective tax rate	22.80%	28.10%	24.40%	27.00%
Deferred Tax Assets, Valuation Allowance	$ 0		$ 0
Decrease in Unrecognized Tax Benefits is Reasonably Possible	0.6		0.6
Accrued interest and penalties	$ 0.1		$ 0.1		$ 0.3
Year subject to examination			2015
State and Local Jurisdiction [Member] | Minimum [Member]
Income Tax Contingency [Line Items]
Year under income tax examination			2014
State and Local Jurisdiction [Member] | Maximum [Member]
Income Tax Contingency [Line Items]
Year under income tax examination			2019

Accounts Receivable Securitiz_3

Accounts Receivable Securitization (Details) - USD ($) $ in Thousands		Sep. 30, 2021	Apr. 23, 2021	Dec. 31, 2020	Jul. 11, 2018	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Servicing Liabilities at Fair Value [Line Items]
Program fees						$ 800	$ 700	$ 2,300	$ 2,800
2018 RSA [Member]
Servicing Liabilities at Fair Value [Line Items]
Effective date					Jul. 11, 2018
Final maturity date					Jul. 9, 2021
Receivables Sales Agreement, Borrowing Capacity					$ 325,000
Accordion Option Accounts Receivable Securitization	[1]				$ 175,000
Unused commitment fee rate					20 to 40 basis points
Program fees on outstanding balances	[2],[3]				one-month LIBOR + 80 to 100 basis points
Accounts receivable securitization – less current portion				$ 302,700
Accounts receivable securitization	[4]			(214,000)
Letters of Credit Outstanding, Amount				(67,281)
Availability under accounts receivable securitization facilities				21,419
Deferred loan costs				$ 100
Debt Instrument, Interest Rate During Period				1.00%
2021 RSA
Servicing Liabilities at Fair Value [Line Items]
Effective date			Apr. 23, 2021
Final maturity date			Apr. 23, 2024
Receivables Sales Agreement, Borrowing Capacity			$ 400,000
Accordion Option Accounts Receivable Securitization	[1]		$ 100,000
Unused commitment fee rate	[5]		20 to 40 basis points
Program fees on outstanding balances	[2]		one-month LIBOR + 82.5 basis points
Accounts receivable securitization – less current portion		$ 400,000				400,000		400,000
Accounts receivable securitization	[4]	(279,000)				(279,000)		(279,000)
Letters of Credit Outstanding, Amount		(65,300)				(65,300)		(65,300)
Availability under accounts receivable securitization facilities		55,700				55,700		55,700
Deferred loan costs		$ 600				$ 600		$ 600
Debt Instrument, Interest Rate During Period		0.90%
[1]	The accordion option increases the maximum borrowing capacity, subject to participation of the purchasers.
[2]	As identified within the 2021 RSA, the lender can trigger an amendment by identifying and deciding upon a replacement for LIBOR.
[3]	Only the rate for the 2018 RSA program fee is subject to the Company's consolidated total net leverage ratio.
[4]	As of September 30, 2021, outstanding borrowings are included in "Accounts receivable securitization – less current portion" in the condensed consolidated balance sheets and are offset by $0.6 million of deferred loan costs. As of December 31, 2020, outstanding borrowings are included in "Accounts receivable securitization – current portion" in the condensed consolidated balance sheets and are offset by $0.1 million of deferred loan costs . Interest accrued on the aggregate principal balance at a rate of 0.9% and 1.0% as of September 30, 2021 and December 31, 2020, respectively.
[5]	The 2021 RSA and 2018 RSA commitment fees rate are based on the percentage of the maximum borrowing capacity utilized.

Debt And Financing - (Details)

Debt And Financing - (Details) - USD ($) $ in Thousands		Sep. 30, 2021	Sep. 03, 2021	Jul. 06, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-Term Debt		$ 1,250,750			$ 298,907
Unsecured Debt, Current		(12,728)			0
Long-term debt – less current portion		1,238,022			298,907
Revolving line of credit		300,000			210,000
Long-term Debt		1,550,750			508,907
2021 Term Loan A-1
Debt Instrument [Line Items]
Long-Term Debt	[1],[2]	199,588			0
Line of Credit Facility, Maximum Borrowing Capacity			$ 200,000
Final maturity date			Dec. 3, 2022
Program fees on outstanding balances			BSBY
Minimum principal payment — amount			$ 0
Minimum principal payment — frequency			Once
Minimum principal payment — commencement date			Dec. 3, 2022
2021 Term Loan A-1 | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3]		0.75%
2021 Term Loan A-1 | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3]		1.38%
2021 Term Loan A-2
Debt Instrument [Line Items]
Long-Term Debt	[1],[2]	199,571			0
Line of Credit Facility, Maximum Borrowing Capacity			$ 200,000
Final maturity date			Sep. 3, 2024
Program fees on outstanding balances			BSBY
Minimum principal payment — amount			$ 0
Minimum principal payment — frequency			Once
Minimum principal payment — commencement date			Sep. 3, 2024
2021 Term Loan A-2 | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3]		0.75%
2021 Term Loan A-2 | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3]		1.38%
2021 Term Loan A-3
Debt Instrument [Line Items]
Long-Term Debt	[1],[2]	798,264			0
Line of Credit Facility, Maximum Borrowing Capacity			$ 800,000
Final maturity date			Sep. 3, 2026
Program fees on outstanding balances			BSBY
Minimum principal payment — amount			$ 10,000
Minimum principal payment — frequency			Quarterly
Minimum principal payment — commencement date			Sep. 30, 2024
2021 Term Loan A-3 | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3]		0.88%
2021 Term Loan A-3 | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3]		1.50%
2017 Term Loan
Debt Instrument [Line Items]
Long-Term Debt	[2],[4]	0			298,907
2021 Prudential Notes
Debt Instrument [Line Items]
Long-Term Debt		47,760			0
Debt Instrument, Unused Borrowing Capacity, Amount		77,100
2021 Prudential Notes | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			4.05%
2021 Prudential Notes | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			4.40%
Other Debt
Debt Instrument [Line Items]
Secured Debt, Other		5,567			0
2021 Revolver
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount		$ 63,800
Line of Credit Facility, Maximum Borrowing Capacity			$ 1,100,000
Final maturity date			Sep. 3, 2026
Program fees on outstanding balances			BSBY
Minimum principal payment — amount			$ 0
Minimum principal payment — frequency			Once
Minimum principal payment — commencement date			Sep. 3, 2026
Debt Instrument, Interest Rate During Period		1.20%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.10%
Line of Credit Facility, Commitment Fee Percentage		1.10%
2021 Revolver | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3],[5]		0.88%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.10%
2021 Revolver | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3],[5]		1.50%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.20%
2017 Revolver
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount					29,300
July 2021 Term Loan
Debt Instrument [Line Items]
Program fees on outstanding balances				BSBY
Debt Instrument, Interest Rate, Stated Percentage				1.00%
2021 Term Loans
Debt Instrument [Line Items]
Debt Instrument, Interest Rate During Period		1.10%
Line of Credit | 2021 Revolver
Debt Instrument [Line Items]
Revolving line of credit	[2],[6]	$ 300,000			0
Line of Credit | 2017 Revolver
Debt Instrument [Line Items]
Revolving line of credit	[2],[7]	0			210,000
Loans Payable [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 2,300,000
Loans Payable [Member] | 2021 Term Loan A-1
Debt Instrument [Line Items]
Deferred loan costs		400
Loans Payable [Member] | 2021 Term Loan A-2
Debt Instrument [Line Items]
Deferred loan costs		400
Loans Payable [Member] | 2021 Term Loan A-3
Debt Instrument [Line Items]
Deferred loan costs		$ 1,700
Loans Payable [Member] | 2017 Term Loan
Debt Instrument [Line Items]
Debt Issuance Costs, Current, Net					$ 1,100
Loans Payable [Member] | 2021 Prudential Notes
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 125,000
Loans Payable [Member] | July 2021 Term Loan
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 1,200,000
[1]	The carrying amounts of the 2021 Term Loan A-1, 2021 Term Loan A-2, and 2021 Term Loan A-3 are net of $0.4 million, $0.4 million, and $1.7 million in deferred loan costs as of September 30, 2021, respectively.
[2]	Refer to Note 15 for information regarding the fair value of debt.
[3]	The interest rate margin for the 2021 Term Loans and 2021 Revolver is based on the Company's consolidated leverage ratio. As of September 30, 2021, interest accrued at 1.1% on the 2021 Term Loans and 1.2% on the 2021 Revolver.
[4]	Net of $1.1 million deferred loan costs at December 31, 2020.
[5]	The commitment fee for the unused portion of the 2021 Revolver is based on the Company's consolidated leverage ratio, and ranges from 0.1% to 0.2%. As of September 30, 2021, commitment fees on the unused portion of the 2021 Revolver accrued at 0.1% and outstanding letter of credit fees accrued at 1.1%.
[6]	The Company also had outstanding letters of credit of $63.8 million under the 2021 Revolver, primarily related to workers' compensation and self-insurance liabilities at September 30, 2021. Subsequent to September 30, 2021, we paid $95.0 million on the 2021 Revolver.
[7]	The Company also had outstanding letters of credit of $29.3 million under the 2017 Revolver, primarily related to workers' compensation and self-insurance liabilities at December 31, 2020.

Debt And Financing - Subsequent

Debt And Financing - Subsequent Event - (Details) $ in Millions	1 Months Ended
	Oct. 29, 2021USD ($)
Subsequent Event [Member] | 2021 Revolver | Line of Credit
Debt Instrument [Line Items]
Repayments of Debt	$ 95

Defined Benefit Pension Plan (D

Defined Benefit Pension Plan (Details) $ in Thousands	3 Months Ended
	Sep. 30, 2021USD ($)
Retirement Benefits [Abstract]
Projected benefit obligation	$ 71,263
Total pension plan assets	69,400
Unfunded status	1,863
Accrued pension liability recognized 1	1,863	[1]
Amount Recorded in Other Comprehensive Income (Loss)	900
Net periodic pension income	596
Benefits paid	$ 771
Discount Rate (Point in Time)	2.53%
Discount Rate (Period of Time)	2.49%
Expected long-term rate of return on pension plan assets	6.00%
Contributions During the Period	$ 0
Defined Benefit Plan, Expected Loss, Next Fiscal Year	0
Remainder of 2021	874
2022	3,593
2023	3,707
2024	3,851
2025	3,953
2026	4,040
2027 through 2030	16,453
Total	$ 36,471
[1]	The pension liability is included in "Other long-term liabilities" in the condensed consolidated balance sheets.

Defined Benefit Pension Plan, A

Defined Benefit Pension Plan, Asset Allocation (Details)	Sep. 30, 2021
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Plan Assets, Actual Allocation	100.00%
Plan Assets, Target Allocation	100.00%
Defined Benefit Plan, Equity Securities
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Plan Assets, Actual Allocation	30.00%
Plan Assets, Target Allocation	30.00%
Defined Benefit Plan, Debt Security
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Plan Assets, Actual Allocation	69.00%
Plan Assets, Target Allocation	70.00%
Defined Benefit Plan, Cash and Cash Equivalents
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Plan Assets, Actual Allocation	1.00%

Commitments (Details)

Commitments (Details) $ in Millions	Sep. 30, 2021USD ($)
Capital Addition Purchase Commitments Total Revenue Equipment [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, to be Paid, Year Two	$ 65.9
Purchase Obligation, to be Paid, Year Three	0
Purchase Obligation, Due in Fourth and Fifth Year	0
Purchase Obligation, Due after Fifth Year	0
Purchase Obligation, to be Paid, Year One	256.7
Capital Addition Purchase Commitments of Tractors [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, to be Paid, Year Two	7.5
Purchase Obligation, to be Paid, Year One	166.8
Capital Addition Purchase Commitments Non revenue equipment [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Future Minimum Payments, Remainder of Fiscal Year	39
Purchase Obligation, Due in Second and Third Year	4.9
Purchase Obligation, Due in Fourth and Fifth Year	0.8
Purchase Obligation, Due after Fifth Year	0
Fuel Purchase Commitment [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Future Minimum Payments, Remainder of Fiscal Year	3.6
Purchase Obligation, Due in Second and Third Year	0
Purchase Obligation, Due in Fourth and Fifth Year	0
Purchase Obligation, Due after Fifth Year	0
Transportation Resource Partners Capital Partners V [Member]
Long-term Purchase Commitment [Line Items]
Additional Amounts Committed To Invest	10
Amounts Committed To Invest	30
Remaining Investment Commitment	20.5
Embark
Long-term Purchase Commitment [Line Items]
Amounts Committed To Invest	25
Remaining Investment Commitment	$ 25

Legal Proceedings (Details)

Legal Proceedings (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Commitments and Contingencies Disclosure [Abstract]
Loss contingency accrual	$ 18.4
Accrual for Environmental Loss Contingencies, Gross	$ 0.4
Employee Compensation and Pay Practices Matters [Member] | CRST Expedited [Member]
Loss Contingencies [Line Items]
Loss contingency, allegations	The plaintiff alleges tortious interference with contract and unjust enrichment related to non-competition agreements entered into with certain of its drivers.
Loss contingency, name of plaintiffs	CRST Expedited, Inc.
Loss contingency, name of defendant	Swift Transportation Co. of Arizona LLC.
Lawsuit filing date	March 20, 2017
Loss contingency, domicile of litigation	United States District Court for the Northern District of Iowa
Loss contingency, opinion of counsel	In July 2019, a jury issued an adverse verdict in this lawsuit. The court issued a decision granting in part and denying in part certain motions related to the jury’s verdict. Both parties have appealed the court’s decision. On August 6, 2021 a three-judge panel of the 8th Circuit Court of Appeals issued an opinion reversing the trial court’s decision. On October 4, 2021 the 8th Circuit Court of Appeals denied a petition for rehearing. The likelihood that a loss has been incurred is no longer probable, and the accrual for this lawsuit has accordingly been reversed as of September 30, 2021.
Employee Compensation and Pay Practices Matters [Member] | California Wage, Meal, and Rest Class Action [Member]
Loss Contingencies [Line Items]
Loss contingency, allegations	The plaintiffs generally allege one or more of the following: that the Company 1) failed to pay the California minimum wage; 2) failed to provide proper meal and rest periods; 3) failed to timely pay wages upon separation from employment; 4) failed to pay for all hours worked; 5) failed to pay overtime; 6) failed to properly reimburse work-related expenses; and 7) failed to provide accurate wage statements.
Loss contingency, opinion of counsel	In April 2019, the parties reached settlement of this matter. In January 2020, the court granted final approval of the settlement. Two objectors appealed the court’s decision granting final approval of the settlement. The likelihood that a loss has been incurred is probable and estimable, and the loss has accordingly been accrued as of September 30, 2021.
Employee Compensation and Pay Practices Matters [Member] | California Wage, Meal, and Rest Class Action [Member] | California Wage, Meal, and Rest Class Action 1 [Member]
Loss Contingencies [Line Items]
Loss contingency, name of plaintiffs	John Burnell 1	[1]
Loss contingency, name of defendant	Swift Transportation Co., Inc
Lawsuit filing date	March 22, 2010
Loss contingency, domicile of litigation	United States District Court for the Central District of California
Employee Compensation and Pay Practices Matters [Member] | California Wage, Meal, and Rest Class Action [Member] | California Wage, Meal, and Rest Class Action 2 [Member]
Loss Contingencies [Line Items]
Loss contingency, name of plaintiffs	James R. Rudsell 1	[1]
Loss contingency, name of defendant	Swift Transportation Co. of Arizona, LLC and Swift Transportation Company
Lawsuit filing date	April 5, 2012
Loss contingency, domicile of litigation	United States District Court for the Central District of California
Independent Contractor Matters [Member] | Ninth circuit owner operator misclassification class action 1 [Member]
Loss Contingencies [Line Items]
Loss contingency, allegations	The putative class alleges that Swift misclassified independent contractors as independent contractors, instead of employees, in violation of the Fair Labor Standards Act and various state laws. The lawsuit also raises certain related issues with respect to the lease agreements that certain independent contractors have entered into with Interstate Equipment Leasing, LLC. The putative class seeks unpaid wages, liquidated damages, interest, other costs, and attorneys' fees.
Loss contingency, name of plaintiffs	Joseph Sheer, Virginia Van Dusen, Jose Motolinia, Vickii Schwalm, Peter Wood 1	[1]
Loss contingency, name of defendant	Swift Transportation Co., Inc., Interstate Equipment Leasing, Inc., Jerry Moyes, and Chad Killebrew
Lawsuit filing date	December 22, 2009
Loss contingency, domicile of litigation	Unites States District Court of Arizona and Ninth Circuit Court of Appeals
Loss contingency, opinion of counsel	In January 2020, the court granted final approval of the settlement in this matter. In March 2020, the Company paid the settlement amount approved by the court. As of September 30, 2021, the Company has accrued for anticipated costs associated with finalizing this matter.
[1]	Individually and on behalf of all others similarly situated.

Self Insurance (Details)

Self Insurance (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Loss Contingencies [Line Items]
Self Insurance Retention	$ 10
Excess coverage layer	5
Excess of excess coverage layer	5
Cargo Insurance per truck or trailer	2
Cargo insurance per occurrence	10
Swift Transportation Company [Member]
Loss Contingencies [Line Items]
Self Insurance Retention	10
Self Insurance Retention Workers Compensation Claims Per Occurrence	5
Self Retention For Employee Medical Health	0.5
Knight Transportation Company [Member]
Loss Contingencies [Line Items]
Insurance Aggregate Deductible Amount	2.5
Self Retention For Employee Medical Health	0.4
Knight Transportation Company [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Self Insurance Retention	1
Knight Transportation Company [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Self Insurance Retention	3
ACT
Loss Contingencies [Line Items]
Self Insurance Retention	2
Insurance Aggregate Deductible Amount	5
Self Insurance Retention Workers Compensation Claims Per Occurrence	1
Self Retention For Employee Medical Health	1
ACT | Maximum [Member]
Loss Contingencies [Line Items]
Insurance Aggregate Deductible Amount	10
Policy Period November 1, 2021 to October 31, 2022
Loss Contingencies [Line Items]
Self Insurance Aggregate Coverage	100
Policy Period November 1, 2020 to October 31, 2021
Loss Contingencies [Line Items]
Self Insurance Aggregate Coverage	100
Policy Period November 1, 2019 to October 31, 2020 [Member]
Loss Contingencies [Line Items]
Self Insurance Aggregate Coverage	130
Policy Period, March 1, 2019 to March 1, 2020 [Member] | Knight Transportation Company [Member]
Loss Contingencies [Line Items]
Excess Personal Injury And Property Damage Liability Insurance	$ 2

Share Repurchase Plans (Details

Share Repurchase Plans (Details) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Nov. 24, 2020	May 30, 2019
Class of Stock [Line Items]
Company shares repurchased				$ 53,661	$ 34,630
Knight-Swift Share Repurchase Plan, May 31, 2019 [Member]
Class of Stock [Line Items]
Share repurchase plan, authorized amount, value								$ 250,000
Share repurchase, shares			0		1,139
Company shares repurchased			$ 0		$ 34,630
Share repurchase plan, remaining authorized amount, value							$ 54,100
Knight-Swift Share Repurchase Plan, November 24, 2020
Class of Stock [Line Items]
Share repurchase plan, authorized amount, value	[1]						$ 250,000
Share repurchase, shares	[1]	0		1,303
Company shares repurchased	[1]	$ 0		$ 53,661
Share repurchase plan, remaining authorized amount, value		$ 196,300		$ 196,300		$ 250,000
[1]	$196.3 million and $250.0 million remained available under the 2020 Knight-Swift Share Repurchase Plan as of September 30, 2021 and December 31, 2020, respectively.

Weighted Average Shares Outst_3

Weighted Average Shares Outstanding (Details) - shares shares in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Basic weighted average common shares outstanding		165,966	170,205	165,823	170,257
Dilutive effect of equity awards		1,140	823	1,113	778
Diluted weighted average common shares outstanding		167,106	171,028	166,936	171,035
Anti-dilutive shares excluded from diluted earnings per share	[1]	23	8	165	187
[1]	Shares were excluded from the dilutive-effect calculation because the outstanding awards' exercise prices were greater than the average market price of the Company's common stock for the periods presented.

Fair Value Measurement - Estima

Fair Value Measurement - Estimated Fair Values (Details) - USD ($) $ in Thousands		Sep. 30, 2021		Dec. 31, 2020
Financial Assets:
Restricted investments, held-to-maturity, amortized cost	[1]	$ 7,140		$ 9,001
Restricted investments, held-to-maturity 1	[1]	7,134		8,995
Equity method investments		82,883		77,562
Equity method investments (Estimated Fair Value)		82,883		77,562
Investments in equity securities		21,063		18,675
Convertible note		37,631		0
Financial Liabilities:
Term loan Carrying Value		1,550,750		508,907
Accounts receivable securitization		278,428		0
Revolving line of credit		300,000		210,000
Business Combination, Contingent Consideration, Liability		21,200		16,200
2017 Term Loan
Financial Liabilities:
Term loan Carrying Value	[2]	0		298,907
Term loan, Fair Value	[2]	0		300,000
2018 RSA [Member]
Financial Liabilities:
Accounts receivable securitization		0		213,918	[3]
RSA, Fair Value Disclosure		0		214,000	[3]
Deferred loan costs				100
2021 RSA
Financial Liabilities:
Accounts receivable securitization		278,428	[4]	0
RSA, Fair Value Disclosure		279,000	[4]	0
Deferred loan costs		600
2017 Revolver
Financial Liabilities:
Revolving line of credit		0		210,000
2021 Revolver
Financial Liabilities:
Revolving line of credit		300,000		0
2021 Term Loan A-1
Financial Liabilities:
Term loan Carrying Value	[5]	199,588		0
Term loan, Fair Value	[5]	200,000		0
2021 Term Loan A-2
Financial Liabilities:
Term loan Carrying Value	[5]	199,571		0
Term loan, Fair Value	[5]	200,000		0
2021 Term Loan A-3
Financial Liabilities:
Term loan Carrying Value	[5]	798,264		0
Term loan, Fair Value	[5]	800,000		0
2021 Prudential Notes
Financial Liabilities:
Term loan Carrying Value	[6]	47,760		0
Term loan, Fair Value	[6]	$ 50,321		0
RSA, Fair Value Disclosure				2,400
Deferred loan costs				$ 100
[1]	Refer to Note 4 for the differences between the carrying amounts and estimated fair values of the Company's restricted investments, held-to-maturity.
[2]	The carrying amount of the 2017 Term Loan is net of $1.1 million in deferred loan costs as of December 31, 2020.
[3]	The carrying amount of the 2018 RSA is net of $0.1 million in deferred loan costs as of December 31, 2020 .
[4]	The carrying amount of the 2021 RSA is net of $0.6 million in deferred loan costs as of September 30, 2021
[5]	The carrying amounts of the 2021 Term Loan A-1, 2021 Term Loan A-2, and 2021 Term Loan A-3 are net of $0.4 million, $0.4 million, and $1.7 million in deferred loan costs as of September 30, 2021, respectively.
[6]	The carrying amount of the 2021 Prudential Notes is net of $0.1 million in deferred loan costs and $2.4 million in fair value adjustments as of September 30, 2021 .

Fair Value Measurement - Recurr

Fair Value Measurement - Recurring and Nonrecurring Measurements (Details) - USD ($) $ in Thousands		3 Months Ended					9 Months Ended
		Sep. 30, 2021		Mar. 31, 2021		Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible note		$ 37,631					$ 37,631			$ 0
Business Combination, Contingent Consideration, Liability		21,200					21,200			16,200
Total pension plan assets		69,400					69,400
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible note		37,631					37,631
Gain (Loss) on Investments		0					12,631
Assets, Fair Value Disclosure		21,063					21,063			18,675
Fair Value, Option, Changes in Fair Value, Gain (Loss)				$ 3,553			11,135
Debt and Equity Securities, Gain (Loss)		4,000					12,800
Debt and Equity Securities, Unrealized Gain (Loss)		3,000				$ 4,400	7,600		$ 6,900
Debt and Equity Securities, Realized Gain (Loss)		1,000					5,200
Business Combination, Contingent Consideration, Liability		21,200	[1]				21,200	[1]		16,200	[2]
Contingent Consideration Gain (Loss)		0		6,730	[2]	0	0	[1]	0
Total pension plan assets		69,400					69,400
Fair Value, Recurring [Member] | US equity funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		14,810					14,810
Fair Value, Recurring [Member] | International equity funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		6,184					6,184
Fair Value, Recurring [Member] | Fixed income funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		47,583					47,583
Fair Value, Recurring [Member] | Cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		823					823
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible note		0					0
Assets, Fair Value Disclosure		21,063					21,063			18,675
Business Combination, Contingent Consideration, Liability		0	[1]				0	[1]		0	[2]
Total pension plan assets		69,400					69,400
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US equity funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		14,810					14,810
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | International equity funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		6,184					6,184
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed income funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		47,583					47,583
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		823					823
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible note		0					0
Assets, Fair Value Disclosure		0					0			0
Business Combination, Contingent Consideration, Liability		0	[1]				0	[1]		0	[2]
Total pension plan assets		0					0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US equity funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		0					0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | International equity funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		0					0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed income funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		0					0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		0					0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible note		37,631					37,631
Assets, Fair Value Disclosure		0					0			0
Business Combination, Contingent Consideration, Liability		21,200	[1]				21,200	[1]		16,200	[2]
Total pension plan assets		0					0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US equity funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		0					0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | International equity funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		0					0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed income funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		0					0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total pension plan assets		0					0
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0					0
Financial and Nonfinancial Liabilities, Fair Value Disclosure		0					0			$ 0
Equipment [Member] | Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	[3]	5,851					5,851
Total Losses, Equipment				$ (5,335)	[3]	$ 0			$ (1,300)
Equipment [Member] | Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	[3]	0					0
Equipment [Member] | Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	[3]	5,851					5,851
Equipment [Member] | Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	[3]	$ 0					$ 0
[1]	The Company did not recognize any gains (losses) during the quarter or year-to-date periods ended September 30, 2021 related to the revaluation of these liabilities. Refer to Note 3 for information regarding the components of these liabilities.
[2]	During the fourth quarter of 2020, the Company increased the estimated fair value of the remaining contingent consideration representing the final two annual payments, resulting in a $6.7 million fair value adjustment of the deferred earnout, which was recorded in “Miscellaneous operating expenses” in the consolidated statement of comprehensive income. The Company did not recognize any losses during the quarter and year-to-date periods ended September 30, 2020
[3]	Reflects the non-cash impairment of certain alternative fuel technology (within the non-reportable segments) and certain revenue equipment held for sale (within the Truckload segment). The Company did not recognize any impairments during the quarter ended September 30, 2020. The Company recognized $1.3 million of impairments during the year-to-date period ended September 30, 2020.

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Receivable		$ 6		$ 6		$ 135
Payable		44		44		51
Freight Services [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift		0	$ 29	0	$ 7,893
Received by Knight-Swift		0	0	0	0
Facility and Equipment Leases [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift		0	27	0	59
Received by Knight-Swift		69	129	214	423
Other Services [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift		8	425	21	459
Received by Knight-Swift		9	2	27	33
Central Freight Lines, Inc. [Member]
Related Party Transaction [Line Items]
Receivable		0		0		133
Payable		0		0		0
Central Freight Lines, Inc. [Member] | Freight Services [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	0	1	0	7,837
Received by Knight-Swift	[1]	0	0	0	0
Central Freight Lines, Inc. [Member] | Facility and Equipment Leases [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	0	25	0	48
Received by Knight-Swift	[1]	0	92	0	277
Central Freight Lines, Inc. [Member] | Other Services [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	0	412	0	427
Received by Knight-Swift	[1]	0	0	0	0
SME Industries [Member] | Freight Services [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	0	28	0	56
Received by Knight-Swift	[1]	0	0	0	0
DPF Mobile [Member]
Related Party Transaction [Line Items]
Receivable		0		0		0
Payable		0		0		41
DPF Mobile [Member] | Other Services [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	0	0	0	0
Received by Knight-Swift	[1]	0	2	0	33
Other Affiliates [Member]
Related Party Transaction [Line Items]
Receivable		6		6		2
Payable		44		44		$ 10
Other Affiliates [Member] | Facility and Equipment Leases [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	0	2	0	11
Received by Knight-Swift	[1]	69	37	214	146
Other Affiliates [Member] | Other Services [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	8	13	21	32
Received by Knight-Swift	[1]	$ 9	$ 0	$ 27	$ 0
[1]	Entities affiliated with former Board member Jerry Moyes include Central Freight Lines, SME Industries, and DPF Mobile. "Other affiliates" includes entities that are associated with various board members and executives and require approval by the Board prior to completing transactions. Transactions with these entities generally include freight services, facility and equipment leases, equipment sales, and other services. • Freight Services Provided by Knight-Swift — The Company charges each of these companies for transportation services. • Freight Services Received by Knight-Swift — Transportation services received from Central Freight Lines represent less-than-truckload freight services rendered to haul parts and equipment to Company shop locations. • Other Services Provided by Knight-Swift — Other services provided by the Company to the identified related parties include equipment sales and miscellaneous services. • Other Services Received by Knight-Swift — Consulting fees, diesel particulate filter cleaning, sales of various parts and tractor accessories, and certain third-party payroll and employee benefits administration services from the identified related parties are included in other services received by the Company. During the quarter ended September 30, 2020, the ownership percentage of Jerry Moyes and related affiliates fell below the threshold requiring related party disclosure. The amounts included in this Note 16 pertain to transactions that occurred prior to the date that the ownership percentage changed.

Information by Segment and Ge_3

Information by Segment and Geography - Segment Financial Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)Segment	Sep. 30, 2020USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment			4
Number of Operating Segments | Segment			23
Total revenue	$ 1,642,445	$ 1,210,406	$ 4,181,160	$ 3,395,902
Operating income (loss)	270,087	165,461	623,461	369,747
Depreciation and amortization of property and equipment	138,570	115,664	382,091	340,486
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenue	1,572,377	1,173,758	4,029,250	3,299,041
Operating income (loss)	260,684	171,509	618,826	386,176
Depreciation and amortization of property and equipment	123,476	101,645	$ 338,822	300,256
Operating Segments [Member] | Truckload [Member]
Segment Reporting Information [Line Items]
Description of products and services			The Truckload reportable segment is comprised of nine truckload operating segments that provide similar transportation services to the Company's customers utilizing similar transportation equipment over both irregular (one-way movement) and/or dedicated routes. The Truckload reportable segment consists of irregular route and dedicated, refrigerated, expedited, flatbed, and cross-border operations.
Total revenue	1,041,332	975,881	$ 2,990,137	2,774,311
Operating income (loss)	206,543	168,781	533,483	383,903
Depreciation and amortization of property and equipment	107,229	97,867	$ 314,320	288,970
Operating Segments [Member] | Logistics [Member]
Segment Reporting Information [Line Items]
Description of products and services			The Logistics reportable segment is comprised of six logistics operating segments that provide similar transportation services to the Company's customers and primarily consist of brokerage and other freight management services utilizing third-party transportation providers and their equipment.
Total revenue	226,338	99,018	$ 511,962	248,320
Operating income (loss)	27,128	2,478	49,061	9,235
Depreciation and amortization of property and equipment	355	214	$ 852	628
Operating Segments [Member] | Intermodal [Member]
Segment Reporting Information [Line Items]
Description of products and services			The Intermodal reportable segment is comprised of two intermodal operating segments that provide similar transportation services to the Company's customers. These transportation services include arranging the movement of customers' freight through third-party intermodal rail services on the Company’s trailing equipment (trailers on flat cars and rail containers), as well as drayage services to transport loads between the railheads and customer locations.
Total revenue	112,801	98,859	$ 335,245	276,410
Operating income (loss)	9,544	250	18,813	(6,962)
Depreciation and amortization of property and equipment	3,942	3,564	$ 11,700	10,658
Operating Segments [Member] | LTL
Segment Reporting Information [Line Items]
Description of products and services			The LTL reportable segment is comprised of one operating segment and provides our customers with regional LTL transportation services through a network of over 70 service centers in the Company's geographical footprint. The Company's LTL service also includes national coverage to customers by utilizing partner carriers for areas outside of the Company's direct network.
Total revenue	191,906	0	$ 191,906	0
Operating income (loss)	17,469	0	17,469	0
Depreciation and amortization of property and equipment	11,950	0	$ 11,950	0
Non-reportable segments [Member]
Segment Reporting Information [Line Items]
Description of all other segments			The non-reportable segments include five operating segments that consist of support services provided to the Company's customers and independent contractors (including repair and maintenance shop services, equipment leasing, warranty services, and insurance), trailer parts manufacturing, warehousing, and certain driving academy activities, as well as certain corporate expenses (such as legal settlements and accruals, certain impairments, and amortization of intangibles related to the 2017 Merger and various acquisitions).
Total revenue	89,393	56,610	$ 206,857	148,141
Operating income (loss)	9,403	(6,048)	4,635	(16,429)
Depreciation and amortization of property and equipment	15,094	14,019	43,269	40,230
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenue	$ (19,325)	$ (19,962)	$ (54,947)	$ (51,280)

Information by Segment and Ge_4

Information by Segment and Geography - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting [Abstract]
Percentages Of Foreign Operations Consolidated Revenue	5.00%	5.00%	5.00%	5.00%
Long lived assets of foreign operations	5.00%		5.00%		5.00%