Knight-Swift Transportation (KNX) 10-K 28 Feb 19 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 20, 2019	Jun. 30, 2018
Entity Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	KNX
Entity Registrant Name	Knight-Swift Transportation Holdings Inc.
Entity Central Index Key	1,492,691
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		173,008,889
Entity Public Float			$ 5,596,886,629
Entity Well-known Seasoned Issuer	Yes
Entity Shell Company	false
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents		$ 82,486	$ 76,649
Cash and cash equivalents — restricted		46,888	73,657
Restricted investments, held to maturity, amortized cost		17,413	22,232
Trade receivables, net of allowance for doubtful accounts of $16,355 and $14,829, respectively		616,830	574,265
Prepaid expenses		67,011	58,525
Assets held for sale		39,955	25,153
Income tax receivable		6,943	55,114
Other Assets, Current		29,706	37,612
Total current assets		907,232	923,207
Property and equipment:
Revenue equipment		2,617,989	2,197,158
Land and land improvements		227,581	216,676
Buildings and building improvements		375,435	357,409
Furniture and fixtures		51,619	43,131
Shop and service equipment		22,771	22,864
Leasehold improvements		10,549	9,905
Total property and equipment		3,305,944	2,847,143
Less: accumulated depreciation and amortization		(693,107)	(462,922)
Property and equipment, net		2,612,837	2,384,221
Goodwill	[1]	2,919,176	2,887,867
Intangible assets, net		1,420,919	1,440,903
Other long-term assets		51,721	47,244
Total assets		7,911,885	7,683,442
Current liabilities:
Accounts payable		117,883	119,867
Accrued payroll and purchased transportation		126,464	107,017
Accrued liabilities		151,500	186,379
Claims accruals – current portion		160,044	147,285
Capital lease obligations and long-term debt – current portion		58,672	49,002
Total current liabilities		614,563	609,550
Revolving line of credit		195,000	125,000
Long-term debt – less current portion		364,590	364,771
Capital lease obligations – less current portion		71,248	127,132
Accounts receivable securitization		239,606	305,000
Claims accruals – less current portion		201,327	206,144
Deferred income taxes		739,538	679,077
Other long-term liabilities		23,294	26,398
Total liabilities		2,449,166	2,443,072
Commitments and contingencies (notes 18, 19, and 20)
Stockholders’ equity:
Preferred stock		0	0
Class A common stock		1,728	1,780
Class B common stock		0	0
Additional paid-in capital		4,242,369	4,219,214
Retained earnings		1,216,852	1,016,738
Total Knight-Swift Stockholders' Equity		5,460,949	5,237,732
Noncontrolling interest		1,770	2,638
Total stockholders’ equity		5,462,719	5,240,370
Total liabilities and stockholders’ equity		$ 7,911,885	$ 7,683,442
[1]	Except for the net accumulated amortization related to deferred tax assets in the Knight Trucking segment, the net carrying amount and gross carrying amount are equal since there are no accumulated impairment losses.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Allowance for Doubtful Accounts Receivable, Current	$ 16,355	$ 14,829
Preferred Stock [Member]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Class A Common Stock [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	172,844,000	177,998,000
Common stock, shares outstanding	172,844,000	177,998,000
Class B Common Stock [Member]
Common stock, par value	$ 0	$ 0.01
Common stock, shares authorized	0	250,000,000
Common stock, shares issued	0	0
Common stock, shares outstanding	0	0

Consolidated Income Statements

Consolidated Income Statements - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating revenue:
Total revenue	$ 5,344,066	$ 2,425,453	$ 1,118,034
Operating expenses:
Salaries, wages, and benefits	1,495,126	688,543	333,929
Fuel	621,997	274,956	129,696
Operations and maintenance	340,627	164,307	76,246
Insurance and claims	215,362	95,199	34,441
Operating taxes and licenses	90,778	40,544	18,728
Communications	20,911	10,691	4,182
Depreciation and amortization of property and equipment	387,505	193,733	115,660
Amortization of intangibles	42,584	13,372	500
Rental expense	177,406	74,224	5,036
Purchased transportation	1,318,303	594,113	233,863
Impairments	2,798	16,844	0
Miscellaneous operating expenses	61,626	41,781	17,274
Merger-related costs	0	16,516	0
Total operating expenses	4,775,023	2,224,823	969,555
Operating income	569,043	200,630	148,479
Other income (expenses):
Interest income	3,200	1,207	309
Interest expense	(30,170)	(8,686)	(897)
Other income, net	9,965	558	4,939
Total other (expenses) income, net	(17,005)	(6,921)	4,351
Income before income taxes	552,038	193,709	152,830
Income tax expense (benefit)	131,389	(291,716)	57,592
Net Income	420,649	485,425	95,238
Net income attributable to noncontrolling interest	(1,385)	(1,133)	(1,375)
Net income attributable to Knight-Swift	$ 419,264	$ 484,292	$ 93,863
Basic earnings per share	$ 2.37	$ 4.38	$ 1.17
Diluted earnings per share	2.36	4.34	1.16
Dividends declared per share:	$ 0.24	$ 0.24	$ 0.24
Shares used in per share calculations
Basic	177,018	110,657	80,362
Diluted	177,999	111,697	81,228
Revenue, excluding fuel surcharge [Member]
Operating revenue:
Total revenue	$ 4,725,288	$ 2,179,873	$ 1,028,148
Fuel surcharge revenue [Member]
Operating revenue:
Total revenue	$ 618,778	$ 245,580	$ 89,886

Consolidated Statements Of Comp

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net Income		$ 420,649	$ 485,425		$ 95,238
Realized gains from available-for-sale securities reclassified to net income	[1]	0	0		(2,771)
Unrealized gains from changes in fair value of available-for-sale securities		0	0	[2]	198	[2]
Other comprehensive income (loss), net of tax		0	0		(2,573)
Comprehensive income, net of income taxes		420,649	485,425		92,665
Comprehensive income attributable to noncontrolling interest		0	0		(1,375)
Comprehensive income attributable to Knight-Swift		$ 420,649	$ 485,425		91,290
Income tax expense related to realized gains from available-for-sale securities reclassified to net income					1,723
Income tax expense (benefit) related to unrealized gains (losses) from changes in fair value of available-for-sale securities					$ 104
[1]	Net of current income tax expense of $1,723 in 2016.
[2]	Net of deferred income tax expense of $104 in 2016.

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Parent [Member]	Noncontrolling Interest [Member]	Class A Common Stock [Member]
Beginning balance at Dec. 31, 2015	$ 740,372	$ 810	$ 205,648	$ 529,367	$ 2,573	$ 738,398	$ 1,974
Beginning balance, shares at Dec. 31, 2015		80,967
Issuance of common stock to employees	13,188	$ 8	13,180			13,188
Issuance of common stock to employees, shares		832
Issuance of common stock to the board of directors	398	$ 0	398			398
Issuance of common stock to the board of directors, shares		15
Company shares repurchased	(39,873)	$ (16)		(39,857)
Company shares repurchased, shares		(1,585)
Shares withheld – restricted stock unit settlement	(1,631)			(1,631)		(1,631)
Stock-based compensation expense	4,041		4,041			4,041
Cash dividends paid and dividends accrued	(19,338)			(19,338)		(19,338)
Net income Attributable to Knight-Swift	93,863			93,863		93,863
Other comprehensive income (loss), net of tax	(2,573)				(2,573)	(2,573)
Distribution to noncontrolling interest	(1,091)						(1,091)
Net income attributable to noncontrolling interest	1,375						1,375
Ending balance at Dec. 31, 2016	788,731	$ 802	223,267	562,404	0	786,473	2,258
Ending balance, shares at Dec. 31, 2016		80,229
2017 Merger reverse split of Swift shares	3,976,905	$ 971	3,975,832			3,976,803	102
2017 Merger reverse split of Swift shares, shares		97,031
Issuance of common stock to employees	13,158	$ 7	13,151			13,158
Issuance of common stock to employees, shares		718
Issuance of common stock to the board of directors	398	$ 0	398			398
Issuance of common stock to the board of directors, shares		12
Shares issued under employee stock purchase plan	324		324			324		$ 0
Shares issued under employee stock purchase plan, shares		8
Shares withheld – restricted stock unit settlement	(4,709)			(4,709)		(4,709)
Stock-based compensation expense	6,242		6,242			6,242
Cash dividends paid and dividends accrued	(25,249)			(25,249)		(25,249)
Net income Attributable to Knight-Swift	484,292			484,292		484,292
Other comprehensive income (loss), net of tax	0
Distribution to noncontrolling interest	(855)						(855)
Net income attributable to noncontrolling interest	1,133						1,133
Ending balance at Dec. 31, 2017	5,240,370	$ 1,780	4,219,214	1,016,738	0	5,237,732	2,638
Ending balance, shares at Dec. 31, 2017		177,998
Issuance of common stock to employees	10,950	$ 6	10,944			10,950
Issuance of common stock to employees, shares		670
Issuance of common stock to the board of directors	774	$ 0	774			774
Issuance of common stock to the board of directors, shares		19
Company shares repurchased	(179,318)			(179,259)		(179,318)		$ (59)
Company shares repurchased, shares								(5,892)
Shares issued under employee stock purchase plan	1,823		1,822			1,823		$ 1
Shares issued under employee stock purchase plan, shares		49
Shares withheld – restricted stock unit settlement	(2,550)			(2,550)		(2,550)
Stock-based compensation expense	11,488		11,488			11,488
Cash dividends paid and dividends accrued	(42,642)			(42,642)		(42,642)
Net income Attributable to Knight-Swift	419,264			419,264		419,264
Other comprehensive income (loss), net of tax	0
Distribution to noncontrolling interest	(2,253)						(2,253)
Net income attributable to noncontrolling interest	1,385						1,385
Net acquisition of remaining ownership interest, previously noncontrolling	(1,873)		(1,873)			(1,873)
Net cumulative-effect adjustment from adopting ASC 606	5,301			5,301		5,301
Ending balance at Dec. 31, 2018	$ 5,462,719	$ 1,728	$ 4,242,369	$ 1,216,852	$ 0	$ 5,460,949	$ 1,770
Ending balance, shares at Dec. 31, 2018		172,844

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Statement of Cash Flows [Abstract]
Net Income	$ 420,649	$ 485,425		$ 95,238
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of property, equipment, and intangibles	430,089	207,105		116,160
Gain on sale of property and equipment	(36,236)	(8,939)		(8,124)
Impairments	2,798	16,844		0
Deferred income taxes	62,469	(305,584)		5,454
Other Noncash Income (Expense)	4,617	14,758	[1]	802
Increase (decrease) in cash resulting from changes in:
Trade receivables	(9,375)	(48,454)		(11,099)
Income Taxes Receivable	48,171	(39,122)		33,561
Accounts payable	(18,033)	(29,890)		3,788
Accrued liabilities and claims accrual	(14,367)	35,820		(2,831)
Other Operating Activities, Cash Flow Statement	(8,805)	(5,373)		10,827
Net cash provided by operating activities	881,977	322,590		243,776
Cash flows from investing activities:
Proceeds from maturities of held-to-maturity investments	26,970	10,730		0
Purchases of held-to-maturity investments	(22,156)	(10,893)		0
Proceeds from sale of property and equipment, including assets held for sale	225,821	82,731		65,595
Purchases of property and equipment	(755,997)	(387,191)		(154,596)
Expenditures on assets held for sale	(30,322)	(1,553)		0
Net cash, restricted cash, and equivalents (invested in) acquired from merger and acquisitions	(101,693)	91,960		0
Other cash flows from investing activities	10,085	9,953	[1]	(12,059)	[2]
Net cash used in investing activities	(647,292)	(204,263)		(101,060)
Cash flows from financing activities:
Repayment of long-term debt and capital leases	(46,630)	(503,153)		0
Proceeds from long-term debt	0	400,000		0
Borrowings (repayments) on revolving lines of credit, net	70,000	107,000		(94,000)
Borrowings under accounts receivable securitization	70,000	40,000		0
Repayments of Accounts Receivable Securitization	135,000	0		0
Proceeds from common stock issued	13,547	13,483		13,188
Payments to repurchase company's common stock	(179,318)	0		(39,873)
Dividends paid	(42,770)	(25,454)		(19,597)
Other cash flows from financing activities	(5,271)	(7,876)		(2,722)
Net cash (used in) provided by financing activities	(255,442)	24,000		(143,004)
Net (decrease) increase in cash, restricted cash, and equivalents	(20,757)	142,327		(288)
Cash, restricted cash, and equivalents at beginning of period	151,733	9,406		9,694
Cash, restricted cash, and equivalents at end of period	130,976	151,733		9,406
Cash paid during the period for:
Interest	28,723	9,286		941
Income taxes	16,106	51,817		18,467
Non-cash investing activities and financing activities
Equipment acquired included in accounts payable	11,931	8,361		3,619
Equipment sales receivables	5,565	350		0
Financing provided to independent contractors for equipment sold	1,742	3,316		1,310
Transfer from property and equipment to assets held for sale	133,434	45,016		30,755
Capital lease additions	$ 0	$ 15,020		$ 0
[1]	See Note 1 for line items that were previously separately presented, but are included in "Other adjustments to reconcile net income to net cash provided by operating activities" and "Other cash flows from investing activities" for the current period presentation.
[2]	See footnote (1) in table above.

Introduction and Basis of Prese

Introduction and Basis of Presentation	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Introduction and Basis of Presentation [Text Block]	Introduction and Basis of Presentation Certain acronyms and terms used throughout this Annual Report are specific to Knight-Swift, 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 2018, we operated an average of 19,156 tractors (comprised of 15,743 company tractors and 3,413 independent contractor tractors) and 69,544 trailers within our Knight Trucking, Swift Truckload, Swift Dedicated, and Swift Refrigerated segments. Additionally, we operated an average of 640 tractors and 9,330 intermodal cont ainers in our Swift Intermodal segment. The Company's six reportable segments are Knight Trucking, Swift Truckload, Swift Dedicated, Swift Refrigerated, Knight Logistics, and Swift Intermodal. Segment Realignment As of the date of this filing, management is re-assessing the presentation of the Company's segment information, which we expect to recast during the first quarter of 2019. Once finalized, the Company will provide recast historical financial results on Knight-Swift's investor website and will file a corresponding Form 8-K with the SEC. Based on management's preliminary assessment, we expect that beginning in the first quarter of 2019, we will present three reportable segments, as follows: • The Trucking Segment will include the results of the previously-reported Knight Trucking, Swift Truckload, Swift Dedicated, and Swift Refrigerated segments. • The Logistics Segment will include the results of the Knight brokerage and Swift logistics businesses which were previously included within the Knight Logistics and Swift non-reportable segments, respectively. • The Intermodal segment will include the results of the previously-reported Swift Intermodal segment and the results of the Knight intermodal business, which was previously included in the Knight Logistics Segment. We expect our non-reportable segments will continue to include support services that Swift's subsidiaries provide to customers and independent contractors (including repair and maintenance shop services, equipment leasing, and insurance), as well as certain legal settlements and accruals, amortization of intangibles related to the 2017 Merger, and certain other corporate expenses. Additionally, we expect our non-reportable segments will include Knight's equipment leasing and warranty services to independent contractors, warehousing activities, and trailer parts manufacturing, which were previously reported within the Knight Logistics segment. 2017 Merger On September 8, 2017, the Company became Knight-Swift Transportation Holdings Inc. upon the effectiveness of the 2017 Merger. Immediately upon the consummation of the 2017 Merger, former Knight stockholders and former Swift stockholders owned approximately 46.0% and 54.0% , respectively, of the Company. Upon closing of the 2017 Merger, the shares of Knight common stock that previously traded under the ticker symbol "KNX" ceased trading and were delisted from the NYSE. The shares of Class A common stock commenced trading on the NYSE on a post-reverse split basis under the ticker symbol "KNX" on September 11, 2017. The Company accounted for the 2017 Merger using the acquisition method of accounting in accordance with GAAP. GAAP requires that either Knight or Swift is designated as the acquirer for accounting and financial reporting purposes ("Accounting Acquirer"). Based on the evidence available, Knight was designated as the Accounting Acquirer while Swift was the acquirer for legal purposes. Therefore, Knight’s historical results of operations replaced Swift’s historical results of operations for all periods prior to the 2017 Merger. More specifically, the accompanying consolidated financial statements for periods prior to the 2017 Merger are those of Knight and its subsidiaries, and for periods subsequent to the 2017 Merger, also include Swift. In identifying Knight as the Accounting Acquirer, management took into account the structure of the 2017 Merger, the composition of the combined company's board of directors and the designation of certain senior management positions of the combined company, among other factors. See Note 5 for further details of the 2017 Merger, including discussion of the purchase price allocation applied, as well as Note 22 for further discussion related to the treatment of the Swift equity awards assumed pursuant to the 2017 Merger. Abilene Acquisition On March 16, 2018, the Company acquired all of the issued and outstanding equity interests of Abilene. Abilene's trucking and logistics businesses are included under the respective Knight segments. Please refer to Note 5 for more information about the Abilene Acquisition. Basis of Presentation The consolidated financial statements include the accounts of Knight-Swift Transportation Holdings Inc. and its subsidiaries. In management's opinion, these consolidated financial statements were prepared in accordance with GAAP and include all adjustments necessary (consisting of normal recurring adjustments) for the fair presentation of the periods presented. With respect to transactional/durational data, references to "years", including "2018", "2017", "2016", "2015", and "2014" pertain to calendar years. Similarly, references to "quarters", including "first", "second", "third", and "fourth" pertain to calendar quarters. Note regarding comparability — Based on the structure of the 2017 Merger, the reported results do not include the results of operations of Swift and its subsidiaries on and prior to the 2017 Merger, in accordance with the accounting treatment applicable to the transaction. Additionally, the reported results do not include the results of operations of Abilene and its subsidiaries on and prior to its acquisition by the Company on March 16, 2018 in accordance with the accounting treatment applicable to the transaction. Accordingly, comparisons between the Company's 2018 results and prior periods may not be meaningful. Joint ventures — The financial activities of the following entities with which the Company has joint ventures are consolidated. The noncontrolling interest for these entities is presented as a separate component of the consolidated financial statements. • In 2014, Knight formed an Arizona limited liability company, now known as Kold Trans, LLC, for the purpose of expanding its refrigerated trucking business. Knight was entitled to 80.0% of the profits of the entity and has effective control over the management of the entity. During 2018, the Company purchased the remaining 20.0% of the joint venture, eliminating the related noncontrolling interest. • In 2010, Knight partnered with a non-related investor to form an Arizona limited liability company for the purpose of sourcing commercial vehicle parts. Knight acquired a 52.0% ownership interest in this entity. Equity and cost method investments — Refer to Note 8 for basis of presentation disclosures regarding Knight's equity and cost method investments in Transportation Resource Partners. Changes in Presentation During 2018, the Company made the following changes in presentation which were attributed to impacts from adopting accounting pronouncements (refer to Note 3 ) and simplifying the presentation of the consolidated balance sheets and statements of cash flows by reclassifying immaterial line items into other line items as indicated below. Balance Sheet - The amounts presented in the Company's 2017 Annual Report were reclassified to align with the December 31, 2018 presentation in this Annual Report as follows: • "Equipment sales receivables" and "Notes receivable, net" were reclassified to "Other current assets." • "Notes receivable, long-term" and "Other long-term assets, restricted cash, and investments" were reclassified to "Other long-term assets." • "Long term debt - current portion" and "Capital lease obligations – current portion" were reclassified to "Capital lease obligations and long-term debt - current portion." • "Dividend payable - current portion" was reclassified to "Accrued liabilities." Statement of Cash Flows - The amounts presented in the Company's 2017 Annual Report and Knight's 2016 Annual Report were reclassified to align with the presentation in this Annual Report as follows: • "Transportation Resource Partners impairment," "Income from investment in TRP Partnerships," "Non-cash compensation expense for issuance of common stock to certain members of the Board of Directors," "Provision for doubtful accounts and notes receivable," "Stock-based compensation expense, net," and "Amortization of debt issue costs, and other" were reclassified to "Other adjustments to reconcile net income to net cash provided by operating activities." • Changes in "Other current assets," "Prepaid expenses," and "Other long-term assets" were reclassified to "Other assets and liabilities." • "Proceeds from notes receivable," "Payments received on equipment sales receivables," "Cash payments to Transportation Resource Partners," and "Cash proceeds from Transportation Resource Partners" were reclassified to "Other cash flows from investing activities." • "Shares withheld for employee taxes related to stock-based compensation," "Cash distribution to noncontrolling interest holder," and "Proceeds from exercise of stock options" were reclassified to "Other cash flows from financing activities." • "Repayments on Knight Revolver" and "Borrowings on Revolver" were reclassified to "Borrowings on revolving lines of credit, net." Income Statement - During 2017, to simplify the presentation of the consolidated income statement, the Company changed its presentation of rental expenses related to revenue equipment, which is now separately presented within "Total operating expenses" in the consolidated income statements. The prior period presentation has been retrospectively adjusted to reclassify the amount out of "Miscellaneous operating expenses" and into the new line item "Rental expense." The change in presentation has no net impact on "Total operating expenses." Seasonality In the 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 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).

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies [Text Block]	Summary of Significant Accounting Policies Use of Estimates — The preparation of the consolidated financial statements, in accordance with GAAP, requires management to make estimates and assumptions about future events that affect the amounts reported in the Company's consolidated financial statements and accompanying notes. On an ongoing basis, management evaluates and periodically adjusts its estimates and assumptions, based on historical experience, the impact of the current economic environment, and other key factors. Volatile energy markets, as well as changes in consumer spending have increased the inherent uncertainty in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Significant items subject to such estimates and assumptions include: • carrying amount of property and equipment, intangibles, and goodwill; • valuation allowances for receivables, inventories, and deferred income tax assets; • valuation of financial instruments; • calculation of stock-based compensation; • estimates of claims accruals; • leases, and • contingent obligations. Segments — The Company uses the "management approach" to determine its reportable segments, as well as to determine the basis of reporting the operating segment information. Certain of the Company's operating segments have been aggregated into reportable segments. The management approach focuses on financial information that management uses to make operating decisions. The Company's chief operating decision makers use total revenue, operating expense categories, operating ratios, operating income, and key operating statistics to evaluate performance and allocate resources to the Company's operations. Operating income is the measure that management uses to evaluate segment performance and allocate resources. Operating income should not be viewed as a substitute for GAAP net income (loss). Management believes the presentation of operating income enhances the understanding of the Company's performance by highlighting the results of operations and the underlying profitability drivers of the business segments. Operating income is defined as "Total revenue" less "Operating expenses." Based on the unique nature of the Company's operating structure, certain revenue-generating assets are interchangeable between segments. Additionally, the Company's chief operating decision makers do not review assets or liabilities by segment to make operating decisions. The Company allocates depreciation and amortization expense of its property and equipment to the segments based on the actual utilization of the asset by the segment during the period. Revenue Disaggregation — In considering the level at which the Company should disaggregate revenues pertaining to contracts with customers, management determined that there are no significant differences between segments in how the nature, amount, timing, and uncertainty of revenue or cash flows are affected by economic factors. Additionally, management considered how and where the Company has communicated information about revenue for various purposes, including disclosures outside of the financial statements and how information is regularly reviewed by the Company's chief operating decision makers for evaluating financial performance of the Company's segments, among others. Based on these considerations, management determined that revenues should be disaggregated by reportable segment. See Note 26 for additional disclosures regarding the Company's segments. Cash and Cash Equivalents — Cash and cash equivalents are comprised of cash, money market funds, and highly liquid instruments with insignificant interest rate risk and original maturities of three months or less. Cash balances with institutions may be in excess of Federal Deposit Insurance Corporation ("FDIC") limits or may be invested in sweep accounts that are not insured by the institution, the FDIC, or any other government agency. Restricted Cash — The Company's wholly-owned captive insurance companies, Red Rock and Mohave, maintain certain operating bank accounts, working trust accounts, and investment accounts. The cash and short-term investments within the accounts are restricted by insurance regulations to fund the insurance claim losses to be paid by the captive insurance companies. Therefore, these cash and short-term investments are classified as "Cash and cash equivalents – restricted" in the consolidated balance sheets. Restricted Investments — The Company's investments are restricted by insurance regulations to fund the insurance claim losses to be paid by the captive insurance companies. The Company accounts for its investments in accordance with ASC 320, Investments – Debt Securities . Management determines the appropriate classification of its investments in debt securities at the time of purchase and re-evaluates the determination on a quarterly basis. As of December 31, 2018 , all of the Company's investments in fixed-maturity securities were classified as held-to-maturity, as the Company has the positive intent and ability to hold these securities to maturity. Held-to-maturity securities are carried at amortized cost. The amortized cost of debt securities is adjusted using the effective interest rate method for amortization of premiums and accretion of discounts. Amortization and accretion are reported in "Other income, net" in the consolidated income statements. Management periodically evaluates restricted investments for impairment. The assessment of whether impairments have occurred is based on management's case-by-case evaluation of the underlying reasons for the decline in estimated fair value. Management accounts for other-than-temporary impairments of debt securities in accordance with ASC 320, Investments – Debt Securities . This guidance requires the Company to evaluate whether it intends to sell an impaired debt security or whether it is more likely than not that it will be required to sell an impaired debt security before recovery of the amortized cost basis. If either of these criteria are met, an impairment loss equal to the difference between the debt security's amortized cost and its estimated fair value is recognized in earnings. For impaired debt securities that do not meet these criteria, the Company determines if a credit loss exists with respect to the impaired security. If a credit loss exists, the credit loss component of the impairment (i.e., the difference between the security's amortized cost and the present value of projected future cash flows expected to be collected) is recognized in earnings and the remaining portion of the impairment is recognized as a component of accumulated other comprehensive income. See Note 7 for additional disclosures regarding the Company's restricted investments. Inventories and Supplies — Inventories and supplies, which are included in "Other current assets" in the consolidated balance sheets, primarily consist of spare parts, tires, fuel, and supplies and are stated at lower of cost or net realizable value. Depending on the class of inventory, cost is determined using the first-in, first-out method or average cost. Property and Equipment — Property and equipment is stated at cost less accumulated depreciation. Costs to construct significant assets include capitalized interest incurred during the construction and development period. Expenditures for replacements and improvements are capitalized. Maintenance and repairs are expensed as incurred. Depreciation of property and equipment is calculated on a straight-line basis down to the salvage value, as applicable, over the following estimated useful lives: Category: Range (in years) Revenue equipment 4 — 20 Shop and service equipment 2 — 10 Land improvements 5 — 15 Buildings and building improvements 10 — 40 Furniture and fixtures 3 — 10 Leasehold improvements Life of the lease Net gains on the disposal of property and equipment are presented in the consolidated income statements within "Miscellaneous operating expenses." Tires on purchased revenue equipment are capitalized along with the related equipment cost when the vehicle is placed in service, and are depreciated over the life of the vehicle. Replacement tires are classified as inventory and expensed when placed in service. Management evaluates its property and equipment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable in accordance with ASC 360, Property, Plant and Equipment . When such events or changes in circumstances occur, management performs a recoverability test that compares the carrying amount with the projected undiscounted cash flows from the use and eventual disposition of the asset or asset group. An impairment is recorded for any excess of the carrying amount over the estimated fair value. Fair value is determined through various valuation techniques including discounted cash flow models, quoted market values, and third-party independent appraisals, as considered necessary. Intangible Assets other than Goodwill — The Company's intangible assets other than goodwill primarily consist of acquired customer relationships and trade names from the 2017 Merger, as well as intangibles from Knight's 2018 acquisition of Abilene, and Knight's 2014 acquisition of Barr-Nunn Transportation, Inc. and certain of its affiliates. Amortization of acquired customer relationships is calculated on a straight-line basis over the estimated useful life, which ranges from 5 years to 20 years . The trade names have indefinite useful lives and are not amortized, but are tested for impairment at least annually, unless events occur or circumstances change between annual tests that would more likely than not reduce the fair value. Management reviews its intangible assets for impairment whenever events or circumstances indicate that the carrying amount of the asset may not be recoverable, in accordance with ASC 350, Intangibles – Goodwill and Other. When such events or changes in circumstances occur, management performs a recoverability test that compares the carrying amount with the projected discounted cash flows from the use and eventual disposition of the asset or asset group. An impairment is recorded for any excess of the carrying amount over the estimated fair value, which is generally determined using discounted future cash flows. See Notes 5 and 12 for additional disclosures regarding the Company's intangible assets. Goodwill — Management evaluates goodwill on an annual basis as of June 30 th , or more frequently if indicators of impairment exist. The Company assesses qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than the carrying amount. If the Company concludes that it is more likely than not that the fair value of a reporting unit is less than its carrying amount, the Company conducts a two -step quantitative goodwill impairment test. The first step of the quantitative impairment test involves comparing the fair values of the applicable reporting units with their carrying values. Management estimates the fair values of its reporting units using a combination of the income and market approaches. If the carrying amount of a reporting unit exceeds the reporting unit's fair value, then management performs the second step of the quantitative impairment test. The second step of the quantitative impairment test involves comparing the implied fair value of the affected reporting unit's goodwill with the carrying value of that goodwill. Any amount by which the carrying value of the goodwill exceeds its implied fair value is recognized as an impairment loss. Refer to Note 12 for discussion of the results of the Company's annual evaluation as of June 30, 2018 . See Notes 5 and 12 for additional disclosures regarding the Company's goodwill. Claims Accruals — The Company is self-insured for a portion of its risk related to auto liability, workers' compensation, property damage, and cargo damage. Self-insurance results from buying insurance coverage that applies in excess of a retained portion of risk for each respective line of coverage. The Company accrues for the cost of the uninsured portion of pending claims by evaluating the nature and severity of individual claims and by estimating future claims development based upon historical claims development trends. The actual cost to settle self-insured claim liabilities may differ from the Company's reserve estimates due to legal costs, claims that have been incurred but not reported, and various other uncertainties, including the inherent difficulty in estimating the severity of the claims and the potential judgment or settlement amount to dispose of the claim. See Notes 14 and 20 for additional disclosures regarding the Company's claims accruals. Operating Leases — In accordance with ASC 840, Leases , property and equipment held under operating leases, and liabilities related thereto, are off-balance sheet. All expenses related to operating leases are reflected in the consolidated income statements in "Rental expense." At lease inception, management determines whether the lease should be classified as operating or capital lease, based on the guidance set forth in ASC 840. Additionally at lease inception, management determines the useful life and estimates residual values of the related equipment. Future minimum lease payments used in determining lease classification represent the minimum rental payments called for over the lease term, inclusive of residual value guarantees (if applicable) and amounts that would be required to be paid, if any, by the Company upon default for leases containing subjective acceleration or cross default clauses. In connection with various operating leases, we issued residual value guarantees, which provide that if we do not purchase the leased equipment from the lessor at the end of the lease term, we are liable to the lessor for an amount equal to the shortage (if any) between the proceeds from the sale of the equipment and an agreed value. To the extent we believe any manufacturer will refuse or be unable to meet its obligation, we recognize additional rental expense to the extent we believe the fair market value at the lease termination will be less than our obligation to the lessor. We believe that proceeds from the sale of equipment under operating leases would exceed the payment obligation on substantially all operating leases. See Note 18 for additional disclosures regarding the Company's operating leases. Fair Value Measurements — See Note 24 for accounting policies and financial information relating to fair value measurements. Contingencies — See Note 20 for accounting policies and financial information related to contingencies. Revenue Recognition (2018) — The Company adopted ASC 606, Revenue from Contracts with Customers , on January 1, 2018. See Note 3 for the impact of this standard on the Company's revenue recognition accounting policies. • Contract Identification — Management has identified that a legally enforceable contract with its customers is executed by both parties at the point of pickup at the shipper's location, as evidenced by the bill of lading. Although the Company may have master agreements with its customers, these master agreements only establish general terms. There is no financial obligation to the shipper until the load is tendered/accepted and the Company takes possession of the load. • Performance Obligations — The Company's only performance obligation is transportation services. The Company's delivery, accessorial, and dedicated operations truck capacity in its dedicated operations represent a bundle of services that are highly interdependent and have the same pattern of transfer to the customer. These services are not capable of being distinct from one another. For example, the Company generally would not provide accessorial services or truck capacity without providing delivery services. • Transaction Price — Depending on the contract, the total transaction price may consist of mileage revenue, fuel surcharge revenue, accessorial fees, truck capacity, and/or non-cash consideration. Non-cash consideration is measured by the estimated fair value of the non-cash consideration at contract inception. There is no significant financing component in the transaction price, as the Company's customers generally pay within the contractual payment terms of 30 to 60 days. • Allocating Transaction Price to Performance Obligations — The transaction price is entirely allocated to the only performance obligation: transportation services. • Revenue Recognition — The performance obligation of providing transportation services is satisfied over time. Accordingly, revenue is recognized over time. Management estimates the amount of revenue in transit at period end based on the number of days completed of the dispatch (which is generally one to three days for the trucking segments, but can be longer for intermodal operations). Management believes this to be a faithful depiction of the transfer of services because if a load is dispatched, but terminates mid-route and the load is picked up by another carrier, then that carrier would not need to re-perform the services for the days already traveled. Recognizing revenue over time is a change from the Company's past practice, under which revenue was recognized at the point in time that the freight was delivered. Due to this change, the timing of revenue recognition (as well as the related variable costs) between reportable periods will change, compared to revenue recognition under ASC 605, Revenue Recognition . However, the net impact on the Company's results of operations on the current reportable period is immaterial and is expected to continue to be immaterial in future reportable periods. There was no change in management's determination that the Company acts as the principal (rather than the agent) with respect to revenue recognition within its logistics businesses, under ASC 606, compared to ASC 605. Accordingly, the Company continues to recognize revenue on a gross basis, consistent with past practices. Significant judgments involved in the Company's revenue recognition and corresponding accounts receivable balances include: • Measuring in-transit revenue at period end (discussed above). • Estimating the allowance for doubtful accounts. The Company establishes an allowance for doubtful accounts based on historical experience and any known trends or uncertainties related to customer billing and account collectability. Management reviews the adequacy of its allowance for doubtful accounts on a quarterly basis. Uncollectible accounts are written off when deemed uncollectible, and accounts receivable are presented net of an allowance for doubtful accounts. The Company recognizes operating lease revenue from leasing tractors and related equipment to independent contractors. Operating lease revenue from rental operations is recognized as earned, which is straight-lined per the rent schedules in the lease agreements. Losses from lease defaults are recognized as offsets to revenue. Revenue Recognition (2016 and 2017) — In accordance with ASC 605-20-25-13, Services for Freight-in-Transit at the End of a Reporting Period, the Company recognized operating revenue and the related direct costs of such revenue when persuasive evidence of an arrangement existed, the fee was fixed and determinable, and collectability was probable, all of which occurred as of the date the freight was delivered. Credit terms for customer accounts are generally on a net 30 day basis. The Company establishes an allowance for doubtful accounts based on historical experience and any known trends or uncertainties related to customer billing and account collectability. The Company reviews the adequacy of its allowance for doubtful accounts on a quarterly basis. Uncollectible accounts are written off when deemed uncollectible, and accounts receivable are presented net of an allowance for doubtful accounts. Stock-based Compensation — The Company accounts for stock-based compensation expense in accordance with ASC 718, Compensation – Stock Compensation. ASC 718 requires that all share-based payments to employees and non-employee directors, including grants of employee stock options, be recognized in the financial statements based upon a grant-date fair value of an award. The fair value of performance units is estimated using the Monte Carlo Simulation valuation model. Equity awards settled in cash are remeasured at each reporting period and are recognized as a liability in the consolidated balance sheets during the vesting period until settlement. The fair value of stock options is estimated using the Black-Scholes option-valuation model. The Company calculates the number of awards expected to vest as awards granted, less expected forfeitures over the life of the award (estimated at grant date). Compensation expense is recorded on a straight-line basis, by amortizing the grant-date fair value over the requisite service period of the entire award. Unless a material deviation from the assumed forfeiture rate is observed during the term in which the awards are expensed, any adjustment necessary to reflect differences in actual experience is recognized in the period the award becomes payable or exercisable. See Note 22 for additional information relating to the Company's stock compensation plan. Income Taxes — Management accounts for income taxes under the asset and liability method. Accordingly, deferred tax assets and liabilities are recognized for the future tax consequences of events that have been included in the consolidated financial statements. Additionally, deferred tax assets and liabilities are determined based on the differences between the financial statement carrying amounts and respective tax bases of assets and liabilities (using enacted tax rates in effect for the year in which the differences are expected to reverse). The effect on deferred tax assets and liabilities of changes in tax rates is recognized in income in the period that includes the enactment date. Net deferred incomes taxes are classified as noncurrent in the consolidated balance sheets. A valuation allowance is provided against deferred tax assets if the Company determines it is more likely than not that such assets will not ultimately be realized. In making such determinations, the Company considers all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax planning strategies, and recent financial operations. Unrecognized tax benefits are defined as the difference between a tax position taken or expected to be taken in a tax return and the benefit recognized and measured pursuant to ASC 740, Income Taxes . The Company does not recognize a tax benefit for uncertain tax positions unless it concludes that it is more likely than not that the benefit will be sustained on audit (including resolutions of any related appeals or litigation processes) by the taxing authority, based solely on the technical merits of the associated tax position. If the recognition threshold is met, the Company recognizes a tax benefit measured at the largest amount of the tax benefit that, in the management's judgment, is greater than 50% likely to be realized. The Company records expected incurred interest and penalties related to unrecognized tax positions in "Income tax (benefit) expense" in the consolidated income statements. To the extent interest and penalties are not assessed with respect to uncertain tax positions, amounts accrued will be reduced and reflected as a reduction of the overall income tax provision. See Note 15 for additional disclosures regarding the Company's income taxes.

Recently Adopted Accounting Pro

Recently Adopted Accounting Pronouncements (Notes)	12 Months Ended
	Dec. 31, 2018
Accounting Changes and Error Corrections [Abstract]
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements Revenue (ASC 606): ASU 2014-09 — Revenue from Contracts with Customers Summary of the Standard — In May 2014, the FASB issued ASU 2014-09, which established ASC 606, Revenue from Contracts with Customers , and superseded the legacy revenue recognition requirements in ASC 605. The core principle of the new standard is that companies should depict the transfer of promised goods or services to its customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The new standard provides a five-step analysis for companies to apply in determining the timing, method, and amount of revenue recognition to achieve the core principle. The amendments in ASU 2014-09 became effective for public companies for annual reporting periods beginning after December 15, 2017 (in accordance with ASU 2015-14, which deferred the original effective date of ASU 2014-09). Companies may apply the amendments in ASU 2014-09 using the modified retrospective approach or a full retrospective approach, with early adoption permitted. Adoption Method and Approach — The Company adopted ASC 606 on January 1, 2018 by applying the modified retrospective approach, resulting in a cumulative-effect adjustment to retained earnings. See "Cumulative-effect Adjustment," below. Comparative information related to periods prior to January 1, 2018 continues to be reported under the legacy guidance in ASC 605. Five-Step Analysis — Management applied the five-step analysis to the Company's four trucking segments (Knight Trucking, Swift Truckload, Swift Dedicated, and Swift Refrigerated), as well as its intermodal and logistics businesses. The Company's other streams of revenue within Swift's non-reportable segments (specifically its leasing and captive insurance subsidiaries) were determined to be out of the scope of ASC 606. See Note 2 for the Company's revenue recognition policy, including the five-step analysis. Practical Expedients — As permitted under ASU 2014-09 (and related ASUs), management employed the use of certain practical expedients in adopting ASC 606, as follows: • The new guidance was only applied to those contracts that were not completed as of the date the Company adopted the new guidance, rather than to all revenue contracts because application of the practical expedient would not materially affect the Company's results. • The portfolio approach was applied in evaluating and accounting for contract costs, because application of the practical expedient would not materially affect the Company's results. • Remaining performance obligations are not disclosed, as the original expected duration of the contract is one year or less. • Incremental costs related to obtaining contracts are expensed as incurred, as they would otherwise be amortized over less than one year. Contract Balances — $15.6 million and $17.0 million of in-transit revenue balances are included in "Trade receivables, net of allowance for doubtful accounts" in the consolidated balance sheets as of December 31, 2018 and January 1, 2018, respectively. The Company's contract liability balances as of December 31, 2018 and January 1, 2018 were immaterial. Cumulative-effect Adjustment — The cumulative effect of changes made to the Company's consolidated opening balance sheet for the adoption of ASC 606 is presented below. December 31, Opening Balance Adjustments January 1, (in thousands) Assets Trade receivables, net of allowance for doubtful accounts $ 574,265 $ 16,992 $ 591,257 Liabilities Accrued payroll and purchased transportation $ 107,017 $ 9,720 $ 116,737 Accrued liabilities 186,076 201 186,277 Deferred tax liabilities 679,077 1,770 680,847 Equity Retained earnings $ 1,016,738 $ 5,301 $ 1,022,039 Current Period Impact of Adoption — The required quantitative disclosures regarding the current period impact of adopting ASC 606 on the consolidated income statement and balance sheet are presented below. The effect of change amounts are entirely attributed to the in-transit accrual from the Company recognizing revenue over time under ASC 606, compared to recognizing revenue at a point in time under ASC 605. 2018 Income Statement As Reported Under ASC 606 If Reported Under ASC 605 Effect of Change to ASC 606 (in thousands) Revenue Revenue, excluding fuel surcharge $ 4,725,288 $ 4,726,578 $ (1,290 ) Fuel surcharge revenue 618,778 618,878 (100 ) Impact on total revenue (1,390 ) Operating Expenses Salaries, wages, and benefits $ 1,495,126 $ 1,495,480 $ 354 Operations and maintenance 340,627 340,645 18 Purchased transportation 1,318,303 1,318,546 243 Impact on total operating expenses 615 Other Expenses Income tax expense $ 131,389 $ 131,613 $ 224 Impact on net income attributable to Knight-Swift $ (551 ) December 31, 2018 Balance Sheet As Reported Under ASC 606 If Reported Under ASC 605 Effect of Change to ASC 606 (in thousands) Assets Trade receivables, net of allowance for doubtful accounts $ 616,830 $ 601,228 $ 15,602 Liabilities Accrued payroll and purchased transportation $ 126,464 $ 117,341 $ 9,123 Accrued liabilities 151,500 152,506 (1,006 ) Deferred tax liabilities 739,538 736,803 2,735 Equity Retained earnings $ 1,216,852 $ 1,212,102 $ 4,750 The Company's adoption of ASC 606 did not materially affect basic earnings per share, diluted earnings per share, or cash flows from operations. Cash (ASC 230): ASU 2016-18 — Restricted Cash and ASU 2016-15 — Classification of Certain Cash Receipts and Cash Payments Summary of the Standards — The FASB issued ASU 2016-18, Restricted Cash , in November 2016. The amendments in ASU 2016-18 require that a statement of cash flows explains the change during the reporting period in the total of cash, cash equivalents, including restricted cash and restricted cash equivalents. As such, restricted cash and restricted cash equivalents amounts should be included in the beginning and ending cash balances in the reconciliation at the bottom of the statement of cash flows. The FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments, in August 2016. This ASU has several amendments, which are designed to reduce existing diversity in practice of how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The ASU addresses eight specific cash flow issues: 1) debt prepayment or extinguishment costs, 2) settlement of zero-coupon debt instruments, 3) contingent consideration payments made after a business combination, 4) proceeds from settlement of insurance claims, 5) proceeds from settlement of corporate-owned life insurance policies, 6) distributions received from equity method investees, 7) beneficial interests in securitization transactions, and 8) separately identifiable cash flows and application of the predominance principle. Adoption Method and Approach — For public companies, the amendments in these ASUs became effective for annual reporting periods beginning after December 15, 2017. The retrospective transition method is required, with prior periods adjusted to align with the current period presentation. Early adoption was permitted; however, the Company adopted the amendments in these ASUs in the first quarter of 2018. Impact of Adoption — The table below summarizes the impact on the statement of cash flows of adopting ASU 2016-18, including changes made to the statement of cash flows captions. As allowed by the amendments in ASU 2016-15, the Company elected to apply the "Nature of Distribution" approach to classifying cash flows from its equity method investments in Transportation Resource Partners. However, retrospectively applying this approach did not change the presentation of the first quarter 2017 statement of cash flows. There were no other cash flow issues in ASU 2016-15 that impacted the Company's statement of cash flows presentation. 2017 As Reported ASU 2016-15 Reclassifications ASU 2016-18 Reclassifications Adjusted (in thousands) Other adjustments to reconcile net income to net cash provided by operating activities (1) $ 10,737 $ 4,021 $ — $ 14,758 Net cash provided by operating activities 318,569 4,021 — 322,590 (Increase) decrease in cash and cash equivalents - restricted (10,215 ) — 10,215 — Net cash, restricted cash, and equivalents acquired from mergers and acquisitions (2) 28,493 — 63,467 91,960 Other cash flows from investing activities (1) 13,957 (4,021 ) 17 9,953 Net cash used in investing activities (273,941 ) (4,021 ) 73,699 (204,263 ) Net increase in cash, restricted cash, and equivalents $ 68,628 $ — $ 73,699 $ 142,327 Cash, restricted cash, and equivalents at beginning of period 8,021 — 1,385 9,406 Cash, restricted cash, and equivalents at end of period $ 76,649 $ — $ 75,084 $ 151,733 (1) See Note 1 for line items that were previously separately presented, but are included in "Other adjustments to reconcile net income to net cash provided by operating activities" and "Other cash flows from investing activities" for the current period presentation. (2) The caption, as previously filed, was "Cash and cash equivalents received with 2017 Merger." 2016 As Reported ASU 2016-15 Reclassifications ASU 2016-18 Reclassifications Adjusted (in thousands) Other adjustments to reconcile net income to net cash provided by operating activities (1) $ 380 $ 422 $ — $ 802 Net cash provided by operating activities 243,354 422 — 243,776 (Increase) decrease in cash and cash equivalents - restricted (6 ) — 6 — Other cash flows from investing activities (1) (12,013 ) (422 ) 376 (12,059 ) Net cash (used in) provided by investing activities (101,020 ) (422 ) 382 (101,060 ) Net (increase) decrease in cash, restricted cash, and equivalents $ (670 ) $ — $ 382 $ (288 ) Cash, restricted cash, and equivalents at beginning of period 8,691 — 1,003 9,694 Cash, restricted cash, and equivalents at end of period $ 8,021 $ — $ 1,385 $ 9,406 (1) See footnote (1) in table above. Reconciliation of Cash, Restricted Cash, and Equivalents — The following table reconciles cash, restricted cash, and equivalents per the consolidated statements of cash flows to the consolidated balance sheets. December 31, December 31, December 31, (in thousands) Balance Sheets Cash and cash equivalents $ 82,486 $ 76,649 $ 8,021 Cash and cash equivalents – restricted 46,888 73,657 — Other long-term assets 1,602 1,427 1,385 Statement of Cash Flows Cash, restricted cash, and equivalents $ 130,976 $ 151,733 $ 9,406 Income Taxes (ASC 740): ASU 2018-05 — Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 Summary of the Standard — The FASB issued ASU 2018-05, Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 ("SAB 118") , in March 2018. ASU 2018-05 provides clarification to address uncertainty or diversity in views about the application of ASC 740 in the period of enactment. Current Period Impact of Adoption — During 2018, the Company updated estimated provisional amounts previously reported as follows: Not long after the passage of the Act, the SEC released SAB 118 to provide relief for tax reform recognition in year-end financial statements. The guidance outlines that where the income tax effects of the Act for which an entity has not completed the accounting by the time the registrant issues its financial statements but a reasonable estimate can be determined, that estimate should be reported as a provisional amount in the financial statements during a “measurement period.” The measurement period is now closed. • Under Internal Revenue Code Section 965, the Transition Tax for the year ending December 31, 2017 was calculated to be $3.2 million . During the SAB 118 measurement period there was an adjustment of $0.3 million increase to the Transition Tax. • The statutory rate change impact was a benefit of $367.0 million . During the SAB 118 measurement period there were temporary difference adjustments resulting from tax returns filed and purchase accounting changes. The tax returns filed utilized $2.9 million of favorable temporary differences at the higher historical federal tax rate. The rate change for the tax return adjustments resulted in $0.4 million increased benefit that was a discrete item in 2018. In addition, purchase accounting adjustments to establish additional $6.5 million of legal reserves were established in 2018 at the higher historical federal tax rate. The rate change for the purchase accounting adjustments resulted in $0.9 million increased expense that was a discrete item in 2018. Other ASUs There were various other ASUs that became effective in the first quarter of 2018, which did not have a material impact on the Company's results of operations, financial position, cash flows, or disclosures. Recently Issued Accounting Pronouncements , Not Yet Adopted Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact December 2018 2018-20: Leases – (Topic 842) Narrow-Scope Improvements for Lessors The amendments in this ASU provide entities with additional guidance about the recognition of variable payments for contracts with lease and nonlease components. These amendments provide lessors the option to exclude certain lessor costs from recognition. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below November 2018 2018-19: Codification Improvements to Topic 326 – Financial Instruments – Credit Losses The amendments in this ASU make targeted improvements to the implementation guidance in ASU 2016-13. The amendments clarify that receivables arising from operating leases are not within the scope of ASC 326-20, but instead should be accounted for in accordance with Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2020, Modified retrospective Currently under evaluation, but not expected to be material August 2018 2018-15: Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract The amendments align the requirements for capitalizing implementation costs in a hosting arrangement with the guidance for internal-use software, resulting in expensing preliminary or post-implementation project costs and capitalizing certain application development costs. The capitalized costs should be included in the balance sheet line that includes prepayment for the fees of the associated hosting arrangement, and amortized over the noncancellable period of the arrangement. Amortization expense should be included in the income statement line that includes the fees associated with the hosting element of the arrangement. Payments for capitalized implementation costs should be classified in the statement of cash flows in the same manner as payments made for hosting element fees. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2020, Prospective Currently under evaluation, but not expected to be material August 2018 2018-13: Fair Value Measurement (Topic 820): Disclosure Framework – Change to the Disclosure Requirements for Fair Value Measurement The amendments in this ASU modify several disclosure requirements under Topic 820. These changes include removing the disclosure requirements related to the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, and adding disclosure requirements about the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Additionally, the amendments remove the phrase "at a minimum" from the codification clarifying that materiality should be considered when evaluating disclosure requirements. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2019, Retrospective Not expected to be material (1) Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact July 2018 2018-11: Leases (Topic 842): Targeted Improvements The amendments in this ASU provide entities with an additional transition method for implementing ASC Topic 842, in which entities have the option to apply the new standard at the adoption date, recognizing a cumulative-effect adjustment to the opening balance of retained earnings. Comparative periods would not be restated, and would instead be presented under the legacy ASC Topic 840 guidance. Under certain conditions, the amendments in this ASU also provide lessors a practical expedient regarding separating nonlease components from the associated lease components if the nonlease components would otherwise be accounted for under ASC Topic 606, Revenue from Contracts with Customers. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below July 2018 2018-10: Leases (Topic 842): Codification Improvements This ASU contains various amendments to ASC Topic 842 that clarify the language, remove inconsistencies, and improve upon other issues, including those associated with implementing the new standard. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below June 2018 2018-07: Compensation – Improvements to Nonemployee Share-Based Payment Accounting The amendments in this ASU expand the scope of ASC Topic 718 to include share-based payments to nonemployees, and for public business entities include 1) measuring awards to nonemployees at grant-date fair value, 2) measuring awards to nonemployees at the grant date, 3) for awards with performance conditions granted to nonemployees, assessing the probability of satisfying performance conditions when measuring such awards, and 4) generally subjecting equity-classified awards to the requirements of ASC Topic 718, eliminating the requirement to reassess classification upon vesting. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. January 2019, Modified retrospective Currently under evaluation (2) January 2018 2018-01: Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842 The amendments in this ASU permit entities to elect to exclude land easements which were not previously recorded as leases from the evaluation related to the adoption of ASC Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below January 2017 2017-04: Intangibles – Goodwill and Other (Topic 350) Simplifying the Test for Goodwill Impairment The amendments in this ASU are intended to simplify subsequent measurement of goodwill. The key amendment in the ASU eliminates Step 2 from the goodwill impairment test, in which entities measured a goodwill impairment loss by comparing the implied fair value to the carrying amount of a reporting unit's goodwill. Instead, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value with the carrying amount of a reporting unit and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value. January 2020, prospective Currently under evaluation; not expected to be material Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact June 2016 2016-13: Financial Instruments – Credit Losses (Topic 326) – Measurement of Credit Losses on Financial Instruments The purpose of this ASU is to amend the current incurred loss impairment methodology with a new methodology that reflects expected credit losses and requires a broader range of reasonable and supportable information to inform credit loss estimates. This is the final credit accounting standard, out of a series, with detailed guidance on the new loss reserve model, Current Expected Credit Loss ("CECL"). Among other provisions, the amendments in the ASU require a financial asset (or group of assets) measured at amortized cost basis to be presented at the net amount expected to be collected. Entities are no longer required to wait until a loss is probable to record it. January 2020, Adoption method varies by amendment Currently under evaluation; not expected to be material February 2016 2016-02: Leases (Topic 842) The new standard requires lessees to recognize assets and liabilities arising from both operating and financing leases on the balance sheet. Lessor accounting for leases is largely unaffected. For public business entities, the new standard is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. January 2019, Modified retrospective - cumulative-effect adjustment to beginning balance of retained earnings at the adoption date Expected to be material (3) (1) ASU 2018-13: Fair Value Measurement (Topic 820): Disclosure Framework – Change to the Disclosure Requirements for Fair Value Measurement — Upon adoption, management expects to have fewer disclosures regarding its fair value measurements as a result of the amendments that eliminate "at a minimum" from the phrase, "an entity shall disclose at a minimum." The amendments are intended to allow entities to exercise discretion when considering fair value disclosures, including materiality considerations. Accordingly, the Company will exclude immaterial disclosures regarding fair value measurements from its quarterly and annual reports upon adoption, beginning in the first quarter of 2019. (2) ASU 2018-07: Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting — In accordance with the amendments in this ASU, the Company will be required to measure any nonemployee liability-classified awards that have not been settled by the adoption date and any equity-classified awards for which a measurement date has not been established through a cumulative-effect adjustment to retained earnings as of January 1, 2019. The Company is not expecting a material impact from adopting the amendments in this ASU, as the Company will have no unvested share-based payment awards related to its nonemployee directors as of January 1, 2019. (3) ASC 842, Leases — The Company established an implementation team, which includes support from external experts, to transition the Company from accounting for leases under ASC 840 to accounting for leases under ASC 842. The diagnostic phase of implementing the new standard is complete, and management has selected practical expedients and accounting policies to evaluate the lease population. The Company is substantially complete with the process of extracting and uploading lease data available from existing systems and documents into its new lease software solution. Management expects to elect the package of practical expedients (regarding lease identification, lease classification, and initial direct costs), but not the hindsight practical expedient. Additionally, management expects to elect accounting policies to account for its revenue equipment leases at the portfolio level, to bundle nonlease components with their related lease components (as lessee), and to not recognize a right-of-use asset or lease liability for short-term leases. These policies are not substantially different from the Company’s current accounting policies. After considering the above practical expedient and accounting policy elections, management expects that adopting the new lease standard will result in adding right-of-use assets of $270.0 million to $300.0 million and corresponding lease liabilities of $270.0 million to $300.0 million to the consolidated balance sheet as of January 1, 2019, with the net impact being recorded as a cumulative-effect adjustment to retained earnings, as applicable. The impact of adopting the new lease standard is not expected to be material to the Company’s consolidated income statement, liquidity, or compliance with debt covenants. Since management is continuing to evaluate the impacts of the above standards, disclosures around these preliminary assessments are subject to change.

Recently Issued Accounting Pron

Recently Issued Accounting Pronouncements	12 Months Ended
	Dec. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recently Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements Revenue (ASC 606): ASU 2014-09 — Revenue from Contracts with Customers Summary of the Standard — In May 2014, the FASB issued ASU 2014-09, which established ASC 606, Revenue from Contracts with Customers , and superseded the legacy revenue recognition requirements in ASC 605. The core principle of the new standard is that companies should depict the transfer of promised goods or services to its customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The new standard provides a five-step analysis for companies to apply in determining the timing, method, and amount of revenue recognition to achieve the core principle. The amendments in ASU 2014-09 became effective for public companies for annual reporting periods beginning after December 15, 2017 (in accordance with ASU 2015-14, which deferred the original effective date of ASU 2014-09). Companies may apply the amendments in ASU 2014-09 using the modified retrospective approach or a full retrospective approach, with early adoption permitted. Adoption Method and Approach — The Company adopted ASC 606 on January 1, 2018 by applying the modified retrospective approach, resulting in a cumulative-effect adjustment to retained earnings. See "Cumulative-effect Adjustment," below. Comparative information related to periods prior to January 1, 2018 continues to be reported under the legacy guidance in ASC 605. Five-Step Analysis — Management applied the five-step analysis to the Company's four trucking segments (Knight Trucking, Swift Truckload, Swift Dedicated, and Swift Refrigerated), as well as its intermodal and logistics businesses. The Company's other streams of revenue within Swift's non-reportable segments (specifically its leasing and captive insurance subsidiaries) were determined to be out of the scope of ASC 606. See Note 2 for the Company's revenue recognition policy, including the five-step analysis. Practical Expedients — As permitted under ASU 2014-09 (and related ASUs), management employed the use of certain practical expedients in adopting ASC 606, as follows: • The new guidance was only applied to those contracts that were not completed as of the date the Company adopted the new guidance, rather than to all revenue contracts because application of the practical expedient would not materially affect the Company's results. • The portfolio approach was applied in evaluating and accounting for contract costs, because application of the practical expedient would not materially affect the Company's results. • Remaining performance obligations are not disclosed, as the original expected duration of the contract is one year or less. • Incremental costs related to obtaining contracts are expensed as incurred, as they would otherwise be amortized over less than one year. Contract Balances — $15.6 million and $17.0 million of in-transit revenue balances are included in "Trade receivables, net of allowance for doubtful accounts" in the consolidated balance sheets as of December 31, 2018 and January 1, 2018, respectively. The Company's contract liability balances as of December 31, 2018 and January 1, 2018 were immaterial. Cumulative-effect Adjustment — The cumulative effect of changes made to the Company's consolidated opening balance sheet for the adoption of ASC 606 is presented below. December 31, Opening Balance Adjustments January 1, (in thousands) Assets Trade receivables, net of allowance for doubtful accounts $ 574,265 $ 16,992 $ 591,257 Liabilities Accrued payroll and purchased transportation $ 107,017 $ 9,720 $ 116,737 Accrued liabilities 186,076 201 186,277 Deferred tax liabilities 679,077 1,770 680,847 Equity Retained earnings $ 1,016,738 $ 5,301 $ 1,022,039 Current Period Impact of Adoption — The required quantitative disclosures regarding the current period impact of adopting ASC 606 on the consolidated income statement and balance sheet are presented below. The effect of change amounts are entirely attributed to the in-transit accrual from the Company recognizing revenue over time under ASC 606, compared to recognizing revenue at a point in time under ASC 605. 2018 Income Statement As Reported Under ASC 606 If Reported Under ASC 605 Effect of Change to ASC 606 (in thousands) Revenue Revenue, excluding fuel surcharge $ 4,725,288 $ 4,726,578 $ (1,290 ) Fuel surcharge revenue 618,778 618,878 (100 ) Impact on total revenue (1,390 ) Operating Expenses Salaries, wages, and benefits $ 1,495,126 $ 1,495,480 $ 354 Operations and maintenance 340,627 340,645 18 Purchased transportation 1,318,303 1,318,546 243 Impact on total operating expenses 615 Other Expenses Income tax expense $ 131,389 $ 131,613 $ 224 Impact on net income attributable to Knight-Swift $ (551 ) December 31, 2018 Balance Sheet As Reported Under ASC 606 If Reported Under ASC 605 Effect of Change to ASC 606 (in thousands) Assets Trade receivables, net of allowance for doubtful accounts $ 616,830 $ 601,228 $ 15,602 Liabilities Accrued payroll and purchased transportation $ 126,464 $ 117,341 $ 9,123 Accrued liabilities 151,500 152,506 (1,006 ) Deferred tax liabilities 739,538 736,803 2,735 Equity Retained earnings $ 1,216,852 $ 1,212,102 $ 4,750 The Company's adoption of ASC 606 did not materially affect basic earnings per share, diluted earnings per share, or cash flows from operations. Cash (ASC 230): ASU 2016-18 — Restricted Cash and ASU 2016-15 — Classification of Certain Cash Receipts and Cash Payments Summary of the Standards — The FASB issued ASU 2016-18, Restricted Cash , in November 2016. The amendments in ASU 2016-18 require that a statement of cash flows explains the change during the reporting period in the total of cash, cash equivalents, including restricted cash and restricted cash equivalents. As such, restricted cash and restricted cash equivalents amounts should be included in the beginning and ending cash balances in the reconciliation at the bottom of the statement of cash flows. The FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments, in August 2016. This ASU has several amendments, which are designed to reduce existing diversity in practice of how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The ASU addresses eight specific cash flow issues: 1) debt prepayment or extinguishment costs, 2) settlement of zero-coupon debt instruments, 3) contingent consideration payments made after a business combination, 4) proceeds from settlement of insurance claims, 5) proceeds from settlement of corporate-owned life insurance policies, 6) distributions received from equity method investees, 7) beneficial interests in securitization transactions, and 8) separately identifiable cash flows and application of the predominance principle. Adoption Method and Approach — For public companies, the amendments in these ASUs became effective for annual reporting periods beginning after December 15, 2017. The retrospective transition method is required, with prior periods adjusted to align with the current period presentation. Early adoption was permitted; however, the Company adopted the amendments in these ASUs in the first quarter of 2018. Impact of Adoption — The table below summarizes the impact on the statement of cash flows of adopting ASU 2016-18, including changes made to the statement of cash flows captions. As allowed by the amendments in ASU 2016-15, the Company elected to apply the "Nature of Distribution" approach to classifying cash flows from its equity method investments in Transportation Resource Partners. However, retrospectively applying this approach did not change the presentation of the first quarter 2017 statement of cash flows. There were no other cash flow issues in ASU 2016-15 that impacted the Company's statement of cash flows presentation. 2017 As Reported ASU 2016-15 Reclassifications ASU 2016-18 Reclassifications Adjusted (in thousands) Other adjustments to reconcile net income to net cash provided by operating activities (1) $ 10,737 $ 4,021 $ — $ 14,758 Net cash provided by operating activities 318,569 4,021 — 322,590 (Increase) decrease in cash and cash equivalents - restricted (10,215 ) — 10,215 — Net cash, restricted cash, and equivalents acquired from mergers and acquisitions (2) 28,493 — 63,467 91,960 Other cash flows from investing activities (1) 13,957 (4,021 ) 17 9,953 Net cash used in investing activities (273,941 ) (4,021 ) 73,699 (204,263 ) Net increase in cash, restricted cash, and equivalents $ 68,628 $ — $ 73,699 $ 142,327 Cash, restricted cash, and equivalents at beginning of period 8,021 — 1,385 9,406 Cash, restricted cash, and equivalents at end of period $ 76,649 $ — $ 75,084 $ 151,733 (1) See Note 1 for line items that were previously separately presented, but are included in "Other adjustments to reconcile net income to net cash provided by operating activities" and "Other cash flows from investing activities" for the current period presentation. (2) The caption, as previously filed, was "Cash and cash equivalents received with 2017 Merger." 2016 As Reported ASU 2016-15 Reclassifications ASU 2016-18 Reclassifications Adjusted (in thousands) Other adjustments to reconcile net income to net cash provided by operating activities (1) $ 380 $ 422 $ — $ 802 Net cash provided by operating activities 243,354 422 — 243,776 (Increase) decrease in cash and cash equivalents - restricted (6 ) — 6 — Other cash flows from investing activities (1) (12,013 ) (422 ) 376 (12,059 ) Net cash (used in) provided by investing activities (101,020 ) (422 ) 382 (101,060 ) Net (increase) decrease in cash, restricted cash, and equivalents $ (670 ) $ — $ 382 $ (288 ) Cash, restricted cash, and equivalents at beginning of period 8,691 — 1,003 9,694 Cash, restricted cash, and equivalents at end of period $ 8,021 $ — $ 1,385 $ 9,406 (1) See footnote (1) in table above. Reconciliation of Cash, Restricted Cash, and Equivalents — The following table reconciles cash, restricted cash, and equivalents per the consolidated statements of cash flows to the consolidated balance sheets. December 31, December 31, December 31, (in thousands) Balance Sheets Cash and cash equivalents $ 82,486 $ 76,649 $ 8,021 Cash and cash equivalents – restricted 46,888 73,657 — Other long-term assets 1,602 1,427 1,385 Statement of Cash Flows Cash, restricted cash, and equivalents $ 130,976 $ 151,733 $ 9,406 Income Taxes (ASC 740): ASU 2018-05 — Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 Summary of the Standard — The FASB issued ASU 2018-05, Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 ("SAB 118") , in March 2018. ASU 2018-05 provides clarification to address uncertainty or diversity in views about the application of ASC 740 in the period of enactment. Current Period Impact of Adoption — During 2018, the Company updated estimated provisional amounts previously reported as follows: Not long after the passage of the Act, the SEC released SAB 118 to provide relief for tax reform recognition in year-end financial statements. The guidance outlines that where the income tax effects of the Act for which an entity has not completed the accounting by the time the registrant issues its financial statements but a reasonable estimate can be determined, that estimate should be reported as a provisional amount in the financial statements during a “measurement period.” The measurement period is now closed. • Under Internal Revenue Code Section 965, the Transition Tax for the year ending December 31, 2017 was calculated to be $3.2 million . During the SAB 118 measurement period there was an adjustment of $0.3 million increase to the Transition Tax. • The statutory rate change impact was a benefit of $367.0 million . During the SAB 118 measurement period there were temporary difference adjustments resulting from tax returns filed and purchase accounting changes. The tax returns filed utilized $2.9 million of favorable temporary differences at the higher historical federal tax rate. The rate change for the tax return adjustments resulted in $0.4 million increased benefit that was a discrete item in 2018. In addition, purchase accounting adjustments to establish additional $6.5 million of legal reserves were established in 2018 at the higher historical federal tax rate. The rate change for the purchase accounting adjustments resulted in $0.9 million increased expense that was a discrete item in 2018. Other ASUs There were various other ASUs that became effective in the first quarter of 2018, which did not have a material impact on the Company's results of operations, financial position, cash flows, or disclosures. Recently Issued Accounting Pronouncements , Not Yet Adopted Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact December 2018 2018-20: Leases – (Topic 842) Narrow-Scope Improvements for Lessors The amendments in this ASU provide entities with additional guidance about the recognition of variable payments for contracts with lease and nonlease components. These amendments provide lessors the option to exclude certain lessor costs from recognition. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below November 2018 2018-19: Codification Improvements to Topic 326 – Financial Instruments – Credit Losses The amendments in this ASU make targeted improvements to the implementation guidance in ASU 2016-13. The amendments clarify that receivables arising from operating leases are not within the scope of ASC 326-20, but instead should be accounted for in accordance with Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2020, Modified retrospective Currently under evaluation, but not expected to be material August 2018 2018-15: Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract The amendments align the requirements for capitalizing implementation costs in a hosting arrangement with the guidance for internal-use software, resulting in expensing preliminary or post-implementation project costs and capitalizing certain application development costs. The capitalized costs should be included in the balance sheet line that includes prepayment for the fees of the associated hosting arrangement, and amortized over the noncancellable period of the arrangement. Amortization expense should be included in the income statement line that includes the fees associated with the hosting element of the arrangement. Payments for capitalized implementation costs should be classified in the statement of cash flows in the same manner as payments made for hosting element fees. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2020, Prospective Currently under evaluation, but not expected to be material August 2018 2018-13: Fair Value Measurement (Topic 820): Disclosure Framework – Change to the Disclosure Requirements for Fair Value Measurement The amendments in this ASU modify several disclosure requirements under Topic 820. These changes include removing the disclosure requirements related to the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, and adding disclosure requirements about the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Additionally, the amendments remove the phrase "at a minimum" from the codification clarifying that materiality should be considered when evaluating disclosure requirements. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2019, Retrospective Not expected to be material (1) Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact July 2018 2018-11: Leases (Topic 842): Targeted Improvements The amendments in this ASU provide entities with an additional transition method for implementing ASC Topic 842, in which entities have the option to apply the new standard at the adoption date, recognizing a cumulative-effect adjustment to the opening balance of retained earnings. Comparative periods would not be restated, and would instead be presented under the legacy ASC Topic 840 guidance. Under certain conditions, the amendments in this ASU also provide lessors a practical expedient regarding separating nonlease components from the associated lease components if the nonlease components would otherwise be accounted for under ASC Topic 606, Revenue from Contracts with Customers. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below July 2018 2018-10: Leases (Topic 842): Codification Improvements This ASU contains various amendments to ASC Topic 842 that clarify the language, remove inconsistencies, and improve upon other issues, including those associated with implementing the new standard. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below June 2018 2018-07: Compensation – Improvements to Nonemployee Share-Based Payment Accounting The amendments in this ASU expand the scope of ASC Topic 718 to include share-based payments to nonemployees, and for public business entities include 1) measuring awards to nonemployees at grant-date fair value, 2) measuring awards to nonemployees at the grant date, 3) for awards with performance conditions granted to nonemployees, assessing the probability of satisfying performance conditions when measuring such awards, and 4) generally subjecting equity-classified awards to the requirements of ASC Topic 718, eliminating the requirement to reassess classification upon vesting. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. January 2019, Modified retrospective Currently under evaluation (2) January 2018 2018-01: Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842 The amendments in this ASU permit entities to elect to exclude land easements which were not previously recorded as leases from the evaluation related to the adoption of ASC Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below January 2017 2017-04: Intangibles – Goodwill and Other (Topic 350) Simplifying the Test for Goodwill Impairment The amendments in this ASU are intended to simplify subsequent measurement of goodwill. The key amendment in the ASU eliminates Step 2 from the goodwill impairment test, in which entities measured a goodwill impairment loss by comparing the implied fair value to the carrying amount of a reporting unit's goodwill. Instead, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value with the carrying amount of a reporting unit and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value. January 2020, prospective Currently under evaluation; not expected to be material Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact June 2016 2016-13: Financial Instruments – Credit Losses (Topic 326) – Measurement of Credit Losses on Financial Instruments The purpose of this ASU is to amend the current incurred loss impairment methodology with a new methodology that reflects expected credit losses and requires a broader range of reasonable and supportable information to inform credit loss estimates. This is the final credit accounting standard, out of a series, with detailed guidance on the new loss reserve model, Current Expected Credit Loss ("CECL"). Among other provisions, the amendments in the ASU require a financial asset (or group of assets) measured at amortized cost basis to be presented at the net amount expected to be collected. Entities are no longer required to wait until a loss is probable to record it. January 2020, Adoption method varies by amendment Currently under evaluation; not expected to be material February 2016 2016-02: Leases (Topic 842) The new standard requires lessees to recognize assets and liabilities arising from both operating and financing leases on the balance sheet. Lessor accounting for leases is largely unaffected. For public business entities, the new standard is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. January 2019, Modified retrospective - cumulative-effect adjustment to beginning balance of retained earnings at the adoption date Expected to be material (3) (1) ASU 2018-13: Fair Value Measurement (Topic 820): Disclosure Framework – Change to the Disclosure Requirements for Fair Value Measurement — Upon adoption, management expects to have fewer disclosures regarding its fair value measurements as a result of the amendments that eliminate "at a minimum" from the phrase, "an entity shall disclose at a minimum." The amendments are intended to allow entities to exercise discretion when considering fair value disclosures, including materiality considerations. Accordingly, the Company will exclude immaterial disclosures regarding fair value measurements from its quarterly and annual reports upon adoption, beginning in the first quarter of 2019. (2) ASU 2018-07: Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting — In accordance with the amendments in this ASU, the Company will be required to measure any nonemployee liability-classified awards that have not been settled by the adoption date and any equity-classified awards for which a measurement date has not been established through a cumulative-effect adjustment to retained earnings as of January 1, 2019. The Company is not expecting a material impact from adopting the amendments in this ASU, as the Company will have no unvested share-based payment awards related to its nonemployee directors as of January 1, 2019. (3) ASC 842, Leases — The Company established an implementation team, which includes support from external experts, to transition the Company from accounting for leases under ASC 840 to accounting for leases under ASC 842. The diagnostic phase of implementing the new standard is complete, and management has selected practical expedients and accounting policies to evaluate the lease population. The Company is substantially complete with the process of extracting and uploading lease data available from existing systems and documents into its new lease software solution. Management expects to elect the package of practical expedients (regarding lease identification, lease classification, and initial direct costs), but not the hindsight practical expedient. Additionally, management expects to elect accounting policies to account for its revenue equipment leases at the portfolio level, to bundle nonlease components with their related lease components (as lessee), and to not recognize a right-of-use asset or lease liability for short-term leases. These policies are not substantially different from the Company’s current accounting policies. After considering the above practical expedient and accounting policy elections, management expects that adopting the new lease standard will result in adding right-of-use assets of $270.0 million to $300.0 million and corresponding lease liabilities of $270.0 million to $300.0 million to the consolidated balance sheet as of January 1, 2019, with the net impact being recorded as a cumulative-effect adjustment to retained earnings, as applicable. The impact of adopting the new lease standard is not expected to be material to the Company’s consolidated income statement, liquidity, or compliance with debt covenants. Since management is continuing to evaluate the impacts of the above standards, disclosures around these preliminary assessments are subject to change.

Merger and Acquisition Merger a

Merger and Acquisition Merger and Acquisition	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Merger and Purchase Price Allocation	Merger and Acquisition 2017 Merger On September 8, 2017, pursuant to the Agreement and Plan of Merger, dated as of April 9, 2017, by Swift Transportation Company, Bishop Merger Sub, Inc., a direct wholly owned subsidiary of Swift ("Merger Sub"), and Knight Transportation, Inc., Merger Sub merged with and into Knight, with Knight surviving as a direct wholly owned subsidiary of Swift (the "2017 Merger"). Immediately prior to the effective time of the 2017 Merger (the "Effective Time"), the certificate of incorporation of the Company was amended and restated (the "Amended Company Charter") to reflect, among other things, that: (1) the Company's corporate name changed from "Swift Transportation Company" to "Knight-Swift Transportation Holdings Inc."; and (2) each issued and outstanding share of Class B common stock, par value $0.01 per share, of Swift was converted (the "Class B Conversion") into one share of Class A common stock, par value $0.01 per share, of Swift and immediately thereafter, each issued and outstanding share of Swift Class A common stock (including each share of Swift Class A common stock into which the shares Swift Class B common stock was converted pursuant to the Class B Conversion) was, by means of a reverse stock split (the "Reverse Split"), consolidated into 0.72 of a share of Class A common stock of the Company. No fractional shares of Class A common stock were issued in the Reverse Split, and, in connection with the Reverse Split, holders of Class A common stock became entitled to receive cash in lieu of any fractional shares in accordance with the Amended Company Charter. At the Effective Time, each share of Knight common stock, par value $0.01 per share, of Knight ("Knight Common Stock") issued and outstanding immediately prior to the Effective Time (other than shares held in the treasury of Knight or owned or held, directly or indirectly, by Swift or any wholly owned subsidiary of Swift or Knight, in each case not held in a fiduciary capacity on behalf of a third-party) was converted into the right to receive one share of the Company's Class A common stock. Upon the closing of the 2017 Merger, the shares of Knight common stock that previously traded under the ticker symbol "KNX" on the NYSE ceased trading on, and were delisted from, the NYSE. Shares of the Company's Class A common stock commenced trading on the NYSE, on a post-Reverse Split basis, under the ticker symbol "KNX" on September 11, 2017. In 2017, the Company recorded $16.5 million of direct and incremental costs associated with 2017 Merger-related activities, primarily incurred for legal and professional fees, which were recorded in the "Merger-related costs" line in the consolidated income statements. In association with the 2017 Merger, the Company incurred merger-related bonuses and accelerated stock compensation expense totaling $5.6 million , which is recorded in the "Salaries, wages, and benefits" line in the consolidated income statements. Additionally, the Company incurred $0.9 million in merger-related statutory filing fees and miscellaneous expense, and $0.1 million in independent contractor retention expenses recorded within the "Miscellaneous operating expenses, net" and "Purchased transportation" lines in the consolidated income statements. Purchase Price Allocation Following the consummation of the 2017 Merger, Knight and Swift stockholders owned approximately 46% and 54% , respectively, of the Company. Based on Knight's $40.85 per share closing price on September 8, 2017 and the fair value of Swift equity awards, consisting of outstanding stock options and certain unvested restricted stock units, and noncontrolling interest assumed by the Company totaling $13.2 million , the 0.72 of a combined company share that the Swift stockholders received in respect of each Class A share of Swift had an aggregate fair value of approximately $4.0 billion . The purchase price allocation for the 2017 Merger has been allocated based on estimated fair values of the assets acquired and liabilities assumed at the acquisition date. The purchase price allocation was open for adjustments through the end of the measurement period, which closed one year from the merger date. The following table summarizes the total fair value consideration transferred: (In thousands, except ratio and stock price) Number of Swift shares outstanding at September 8, 2017 134,765 Swift share consolidation ratio 0.72 Swift shares outstanding post-Reverse Split and immediately prior to the 2017 Merger 97,031 Closing price of Knight on September 8, 2017 $ 40.85 Fair value of equity portion of the 2017 Merger consideration $ 3,963,712 Fair value of Swift equity awards and noncontrolling interest assumed 13,193 Total fair value of consideration transferred $ 3,976,905 The following is a summary of the allocation of purchase consideration to the estimated fair value of Swift's assets acquired and liabilities assumed in the 2017 Merger: September 9, 2017 Opening Balance Sheet as Reported at September 30, 2017 Adjustments Adjusted September 9, 2017 Opening Balance Sheet as reported at December 31, 2018 (In thousands) Fair value of the consideration transferred $ 3,976,905 $ — $ 3,976,905 Cash and cash equivalents $ 28,484 $ — $ 28,484 Restricted cash and fixed maturity securities 85,615 — 85,615 Trade and other receivables 411,767 — 411,767 Prepaid expenses 44,564 — 44,564 Other current assets 19,736 — 19,736 Property and equipment 1,522,123 — 1,522,123 Identifiable intangible assets (1) 1,285,900 165,800 1,451,700 Other noncurrent assets 18,537 — 18,537 Total assets 3,416,726 165,800 3,582,526 Accounts payable (188,411 ) — (188,411 ) Accrued liabilities (2) (232,280 ) (6,466 ) (238,746 ) Claims accruals (306,846 ) — (306,846 ) Long-term debt and capital lease obligations (894,681 ) — (894,681 ) Deferred tax liabilities (1) (2) (741,405 ) (61,900 ) (803,305 ) Other long-term liabilities (18,452 ) — (18,452 ) Total liabilities (2,382,075 ) (68,366 ) (2,450,441 ) Goodwill (1) (2) $ 2,942,254 $ (97,434 ) $ 2,844,820 (1) Adjustments made to identifiable intangible assets, goodwill, and deferred tax liabilities pertain to management's re-evaluation of the royalty rate used associated with certain trade names. (2) Adjustments made to accrued liabilities, goodwill, and deferred tax liabilities due to new information obtained related to certain legal matters that were outstanding as of the 2017 Merger closing date. The goodwill is primarily attributable to Swift's existing workforce and the synergies expected to arise after the 2017 Merger. These acquired capabilities, when combined with Knight's business, will result in opportunities that allow us to provide services under contracts that could not have been pursued individually by either Knight or Swift. The Company allocated goodwill to its reportable segments (as presented in Note 12 ). The goodwill will not be deductible for tax purposes. The estimated fair value of the acquired identifiable intangible assets is based on a valuation completed for Swift, along with related tangible assets, using a combination of the income method and comparable market transactions. Following are the details of the preliminary purchase price allocated to the identifiable intangible assets acquired: Estimated Life Estimated Fair Value as of September 9, 2017 Adjustments (1) Adjusted Estimated Fair Value as of September 9, 2017 (years) (thousands) Customer relationships 10 - 20 years $ 817,200 $ (700 ) $ 816,500 Trade name indefinite 468,700 166,500 635,200 Total identifiable intangible assets $ 1,285,900 $ 165,800 $ 1,451,700 (1) See (1), above for nature of the adjustments made to intangible assets. The Company's 2017 consolidated financial statements include Swift's results of operations after September 8, 2017 (closing of the 2017 Merger) through December 31, 2017 . During 2017, Swift's total revenue and net income included within the Company's consolidated operating results was $1.3 billion and $95.7 million , respectively. Swift's net income for this period includes a $16.8 million impairment charge primarily related to termination of implementation of Swift's ERP system, as well as $12.9 million related to the amortization of intangibles acquired in the 2017 Merger. Abilene Acquisition On March 16, 2018, the Company purchased 100.0% of the equity interests of Abilene. Abilene is a diversified truckload carrier located in Richmond, Virginia operating throughout the US and Canada. The total consideration of $103.3 million consisted of approximately $80.5 million in cash consideration to the sellers, plus approximately $22.8 million for debt payoffs. The Company funded the Abilene Acquisition through cash-on-hand and borrowing on the Revolver on the date of the transaction. At closing, $7.0 million of the purchase price was placed in escrow to secure the sellers' indemnification obligations and an additional $4.5 million of the purchase price was placed in escrow in respect of certain tax obligations of the sellers and remains subject to further adjustments . The equity purchase agreement included an election under the 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 equity purchase agreement contains customary representations, warranties, covenants, and indemnification provisions. The results of the acquired business have been included in the consolidated financial statements since the date of acquisition and represent 1.6% of consolidated total revenue, and 2.1% of consolidated net income attributable to Knight-Swift for 2018 . The acquired business also represented 1.7% of consolidated total assets as of December 31, 2018 . The Company recorded approximately $0.2 million of acquisition-related expenses, which are included within "Miscellaneous operating expenses" in the consolidated income statements. The goodwill recognized represents expected synergies from combining the operations of Abilene with the Company, including enhanced service offerings and sharing best practices in terms of driver recruiting and retention, 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. The purchase price allocation for the Abilene Acquisition is preliminary and has been allocated based on estimated fair values of the assets acquired and liabilities assumed at the acquisition date. Certain data necessary to complete the purchase price allocation for the Abilene Acquisition is open for adjustments during the measurement period and includes, but is not limited to, finalization of certain contingent liabilities and 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 the Company obtains more information, the preliminary purchase price allocation disclosed below is subject to change. Any future adjustments to the preliminary purchase price allocation, 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 period, which is not to exceed one year from the acquisition date. The following table summarizes the fair value of the consideration transferred as of the acquisition date, including any adjustments during the measurement period: March 16, 2018 Opening Balance Sheet as Reported at March 31, 2018 Adjustments Adjusted March 16, 2018 Opening Balance Sheet as Reported at December 31, 2018 (in thousands) Fair value of the consideration transferred $ 103,223 $ 124 $ 103,347 Cash 1,654 — 1,654 Trade receivables 11,745 1,265 13,010 Other assets 7,785 842 8,627 Property and equipment 41,403 — 41,403 Identifiable intangible assets (1) 23,000 (400 ) 22,600 Total assets 85,587 1,707 87,294 Accounts payable 1,959 1,577 3,536 Accrued liabilities 2,419 4,942 7,361 Claims accruals 230 172 402 Total liabilities 4,608 6,691 11,299 Goodwill $ 22,244 $ 5,108 $ 27,352 (1) Includes a $17.9 million customer relationship and a $4.7 million trade name. The above adjustments were related to the completion of an independent valuation of certain acquired intangible assets, the identification of liabilities associated with capital expenditures incurred prior to the acquisition, adjustments for Abilene’s adoption of ASC 606, and the associated deferred tax asset impact of these adjustments. No material income statement effects were identified with these adjustments. Consolidated Pro Forma Information The following unaudited pro forma information combines the historical operations of Knight, Swift, and Abilene giving effect to the 2017 Merger, Abilene Acquisition, and related transactions as if they had been consummated on January 1, 2017, the beginning of the comparative periods presented. 2018 2017 (in thousands, except per share data) Total revenue $ 5,366,551 $ 5,230,674 Net income attributable to Knight-Swift $ 419,812 $ 536,062 Diluted earnings per share $ 2.36 $ 3.00 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 Abilene during the periods presented that were directly related to the 2017 Merger and the Abilene Acquisition, and related income tax effects of these items. As a result of the 2017 Merger, Knight and Swift incurred certain merger-related expenses, including professional legal and advisory fees, acceleration of share-based compensation, bonus incentives, severance payments, filing fees, and other miscellaneous expenses. These merger-related expenses for both Knight and Swift totaled $57.0 million in 2017 and are eliminated from presentation of the unaudited pro forma net income presented above. The acquisition-related expenses that Knight incurred from the Abilene Acquisition, discussed above, are eliminated from presentation of the unaudited pro forma net income presented above. The unaudited pro forma condensed combined financial information does not purport to represent the actual results of operations that Knight, Swift, and Abilene 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 2017 Merger and Abilene Acquisition and also does not reflect any restructuring or integration-related costs to achieve those potential cost savings.

Marketable Securities Marketabl

Marketable Securities Marketable Securities	12 Months Ended
	Dec. 31, 2018
Marketable Securities [Abstract]
Marketable Securities	Marketable Securities Historically, Knight, from time to time, held certain marketable equity securities classified as available-for-sale securities, which are recorded at fair value with unrealized gains and losses, net of tax, as a component of "Accumulated other comprehensive income (loss)" in stockholders' equity on the accompanying consolidated balance sheets. Realized gains and losses on available-for-sale securities are included in the determination of net income. Management uses specific identification to determine the cost of securities sold, or amounts reclassified out of accumulated other comprehensive income into earnings and included in "Other income" in the accompanying income statements. The following table shows realized gains during 2018 , 2017 , and 2016 , on certain securities that were classified as available-for-sale: 2018 2017 2016 (In thousands) Realized Gains: Sales proceeds $ — $ — $ 7,403 Cost of securities sold — — 2,909 Realized gain $ — $ — $ 4,494 Realized gain, net of taxes $ — $ — $ 2,771 Knight disposed of its holdings in available-for-sale equity investments in 2016, leaving no balance on the accompanying consolidated balance sheets as of December 31, 2018 or December 31, 2017 .

Restricted Investments, Held-to

Restricted Investments, Held-to-Maturity	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Restricted Investments	Restricted Investments, Held-to-Maturity The following table presents the cost or amortized cost, gross unrealized gains and temporary losses, and estimated fair value of the Company's restricted investments: December 31, 2018 Gross Unrealized Cost or Amortized Cost Gains Temporary Estimated Fair Value (In thousands) US corporate securities $ 15,296 $ 1 $ (16 ) $ 15,281 Municipal bonds 1,082 — — 1,082 Negotiable certificates of deposit 1,035 — — 1,035 Restricted investments, held-to-maturity $ 17,413 $ 1 $ (16 ) $ 17,398 December 31, 2017 Gross Unrealized Cost or Amortized Cost Gains Temporary Estimated Fair Value (In thousands) US corporate securities $ 15,982 $ — $ (14 ) $ 15,968 Municipal bonds 4,970 — (10 ) 4,960 Negotiable certificates of deposit 1,280 — — 1,280 Restricted investments, held-to-maturity $ 22,232 $ — $ (24 ) $ 22,208 As of December 31, 2018 , the contractual maturities of the restricted investments were one year or less. There were 20 and 32 securities that were in an unrealized loss position for less than twelve months as of December 31, 2018 and 2017 , respectively. The Company did not recognize any impairment losses related to restricted investments during 2018 , 2017 , or 2016 . Refer to Note 2 for accounting policy and Note 24 for additional information regarding fair value measurements of restricted investments.

Transportation Resource Partner

Transportation Resource Partners Transportation Resource Partners	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Transportation Resource Partners	Transportation Resource Partners Since 2003, Knight has entered into partnership agreements with entities that make privately-negotiated equity investments, including Transportation Resource Partners ("TRP"), Transportation Resource Partners III, LP ("TRP III"), TRP Capital Partners, LP ("TRP IV"), TRP CoInvest Partners, (NTI) I, LP ("TRP Coinvestment NTI"), and TRP CoInvest Partners, (QLS) I, LP ("TRP Coinvestment QLS"). In these agreements, Knight committed to invest in return for an ownership percentage. In January of 2019, Knight entered a new commitment with TRP for $4.9 million . The following table presents ownership and commitment information for Knight's investments in TRP partnerships: December 31, 2018 Knight's Ownership Interest (5) Total Commitment (All Partners) Knight's Contracted Commitment Knight's Remaining Commitment (Dollars in thousands) TRP – equity investment (1) 2.3 % $ 260,000 $ 5,500 $ — TRP III – equity method investment (2) 5.3 % $ 245,000 $ 15,000 $ 1,715 TRP IV – equity investment (3) (1) 4.1 % $ 116,000 $ 4,900 $ 2,002 TRP Coinvestment NTI – equity method investment (4) 8.3 % $ 120,000 $ 10,000 $ — TRP Coinvestment QLS – equity method investment (4) 25.0 % $ 39,000 $ 9,735 $ — (1) In accordance with ASC 321, Investments – Equity Securities , these investments are recorded at cost minus impairment. (2) Management anticipates that the following amounts will be due: $1.7 million from 2020 through 2021. (3) Management anticipates that the following amounts will be due: $1.0 million in 2019, $0.2 million from 2020 through 2021, $0.2 million from 2022 through 2023, and $0.6 million from 2024 through 2025. (4) The TRP Coinvestments are unconsolidated majority interests. Management considered the criteria set forth in ASC 323, Investments – Equity Method and Joint Ventures , to establish the appropriate accounting treatment for these investments. This guidance requires the use of the equity method for recording investments in limited partnerships where the "so minor" interest is not met. As such, the investments are being accounted for under the equity method. Knight's ownership interest reflects its ultimate ownership of the portfolio companies underlying the TRP Coinvestment NTI and TRP Coinvestment QLS legal entities. (5) Knight's share of the results is included within "Other income, net" in the consolidated income statements. Net investment balances included in "Other long-term assets" in the consolidated balance sheets were as follows: December 31, 2018 2017 (in thousands) TRP – equity investment (1) $ 211 $ 211 TRP III – equity method investment 1,781 1,973 TRP IV – equity investment (1) 2,022 2,577 TRP Coinvestment NTI – equity method investment 5,547 7,579 TRP Coinvestment QLS – equity method investment 11,085 8,054 Total carrying value $ 20,646 $ 20,394 (1) In accordance with ASC 321, Investments – Equity Securities , these investments are recorded at cost minus impairment.

Trade Receivables, net

Trade Receivables, net	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Trades Receivables, net	Trade Receivables, net Trade receivables balances were as follows: December 31, 2018 2017 (In thousands) Trade customers $ 597,077 $ 565,732 Equipment manufacturers 7,166 6,017 Other 28,942 17,345 Trade receivables 633,185 589,094 Less: Allowance for doubtful accounts (16,355 ) (14,829 ) Trade receivables, net (1) $ 616,830 $ 574,265 (1) Includes $15.6 million of in-transit revenue as of December 31, 2018 . The following is a rollforward of the allowance for doubtful accounts for trade receivables: 2018 2017 2016 (In thousands) Beginning balance $ 14,829 $ 2,727 $ 3,106 (Reduction) provision (3,092 ) 4,671 909 Write-offs directly against the reserve (1,362 ) (1,583 ) — Write-offs for revenue adjustments 5,861 (3,758 ) (1,288 ) Other (1) 119 12,772 — Ending balance $ 16,355 $ 14,829 $ 2,727 (1) Increase in allowance for doubtful accounts relates to trade receivables assumed in 2017 from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions. See Note 16 for a discussion of the Company's accounts receivable securitization program and the related accounting treatment. Notes Receivable, net The Company provides financing to independent contractors and other third-parties on equipment sold or leased. Most of the notes are collateralized and are due in weekly installments, including principal and interest payments, ranging from 2% to 20% . Notes receivable are included in "Other current assets" and "Other long-term assets" in the consolidated balance sheets and were comprised of: December 31, 2018 2017 (In thousands) Notes receivable from independent contractors $ 9,318 $ 8,977 Notes receivable from third parties 7,075 7,865 Gross notes receivable 16,393 16,842 Allowance for doubtful notes receivable (1,051 ) (1,040 ) Total notes receivable, net of allowance $ 15,342 $ 15,802 Current portion, net of allowance 4,563 4,742 Long-term portion $ 10,779 $ 11,060 The following is a rollforward of the allowance for doubtful notes receivable: December 31, 2018 2017 2016 (In thousands) Beginning balance $ 1,040 $ 240 $ 273 (Reduction) provision (100 ) 574 (27 ) Write-offs (103 ) (53 ) (6 ) Other (1) 214 279 — Ending balance $ 1,051 $ 1,040 $ 240 (1) Increase in allowance for doubtful notes relates to notes receivable in 2017 assumed from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions.

Notes Receivable, net

Notes Receivable, net	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Notes Receivable, net	Trade Receivables, net Trade receivables balances were as follows: December 31, 2018 2017 (In thousands) Trade customers $ 597,077 $ 565,732 Equipment manufacturers 7,166 6,017 Other 28,942 17,345 Trade receivables 633,185 589,094 Less: Allowance for doubtful accounts (16,355 ) (14,829 ) Trade receivables, net (1) $ 616,830 $ 574,265 (1) Includes $15.6 million of in-transit revenue as of December 31, 2018 . The following is a rollforward of the allowance for doubtful accounts for trade receivables: 2018 2017 2016 (In thousands) Beginning balance $ 14,829 $ 2,727 $ 3,106 (Reduction) provision (3,092 ) 4,671 909 Write-offs directly against the reserve (1,362 ) (1,583 ) — Write-offs for revenue adjustments 5,861 (3,758 ) (1,288 ) Other (1) 119 12,772 — Ending balance $ 16,355 $ 14,829 $ 2,727 (1) Increase in allowance for doubtful accounts relates to trade receivables assumed in 2017 from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions. See Note 16 for a discussion of the Company's accounts receivable securitization program and the related accounting treatment. Notes Receivable, net The Company provides financing to independent contractors and other third-parties on equipment sold or leased. Most of the notes are collateralized and are due in weekly installments, including principal and interest payments, ranging from 2% to 20% . Notes receivable are included in "Other current assets" and "Other long-term assets" in the consolidated balance sheets and were comprised of: December 31, 2018 2017 (In thousands) Notes receivable from independent contractors $ 9,318 $ 8,977 Notes receivable from third parties 7,075 7,865 Gross notes receivable 16,393 16,842 Allowance for doubtful notes receivable (1,051 ) (1,040 ) Total notes receivable, net of allowance $ 15,342 $ 15,802 Current portion, net of allowance 4,563 4,742 Long-term portion $ 10,779 $ 11,060 The following is a rollforward of the allowance for doubtful notes receivable: December 31, 2018 2017 2016 (In thousands) Beginning balance $ 1,040 $ 240 $ 273 (Reduction) provision (100 ) 574 (27 ) Write-offs (103 ) (53 ) (6 ) Other (1) 214 279 — Ending balance $ 1,051 $ 1,040 $ 240 (1) Increase in allowance for doubtful notes relates to notes receivable in 2017 assumed from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions.

Assets Held for Sale

Assets Held for Sale	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment Assets Held-for-sale Disclosure [Abstract]
Assets Held for Sale	Assets Held for Sale The Company expects to sell its assets held for sale within the next twelve months . Revenue equipment held for sale totaled $40.0 million and $25.2 million as of December 31, 2018 and 2017 , respectively. Net gains on disposals, including disposals of property and equipment classified as assets held for sale, reported in "Miscellaneous operating expenses" in the consolidated income statements were $37.0 million during 2018 and $8.9 million during 2017. The Company's net carrying value of land and facilities classified as held for sale in the consolidated balance sheets as of December 31, 2018 and December 31, 2017 was zero . The Company did not recognize any impairment losses related to assets held for sale during 2018, 2017, and 2016 .

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill The changes in the carrying amounts of goodwill were as follows: December 31, 2018 2017 (In thousands) Goodwill at beginning of period $ 2,887,867 $ 47,031 Amortization relating to deferred tax assets (17 ) (10 ) Abilene Acquisition (1) 27,352 — Goodwill related to 2017 Merger (2) 3,974 2,840,846 Goodwill at end of period $ 2,919,176 $ 2,887,867 (1) The goodwill associated with the Abilene Acquisition was allocated to the Knight Trucking segment. See Note 5 regarding the amount attributed to adjustments to the March 17, 2018 opening balance sheet. (2) The goodwill adjustment associated with the 2017 Merger resulted in a $4.8 million increase, a $1.1 million increase, and a $1.9 million decrease in goodwill allocated to the Swift Truckload, Swift Dedicated, and Swift Refrigerated segments, respectively. See Note 5 regarding the nature of the adjustment. The following presents the components of goodwill by segment as of December 31, 2018 and 2017 : December 31, 2018 2017 Net Carrying Amount (1) Net Carrying Amount (1) (In thousands) Swift – Truckload $ 1,154,783 $ 1,150,012 Swift – Dedicated 780,392 779,335 Swift – Refrigerated 648,759 650,613 Swift – Intermodal 175,594 175,594 Swift – Non-reportable 85,292 85,292 Knight – Trucking 74,356 47,021 Goodwill $ 2,919,176 $ 2,887,867 (1) Except for the net accumulated amortization related to deferred tax assets in the Knight Trucking segment, the net carrying amount and gross carrying amount are equal since there are no accumulated impairment losses. There were no impairments identified during annual goodwill impairment testing in 2018 , 2017 , or 2016 . Other Intangible Assets Other intangible asset balances were as follows: December 31, 2018 2017 (In thousands) Customer relationships and non-compete: Gross carrying amount (1) $ 838,100 $ 820,200 Accumulated amortization (57,081 ) (14,497 ) Customer relationships and non-compete, net 781,019 805,703 Trade names: Gross carrying amount (1) 639,900 635,200 Intangible assets, net $ 1,420,919 $ 1,440,903 (1) The changes in the gross carrying amounts of intangible assets are related to the Abilene Acquisition and are discussed in Note 5 . The following table presents amortization of intangible assets related to the 2017 Merger and intangible assets existing prior to the 2017 Merger: 2018 2017 2016 (In thousands) Amortization of intangible assets related to the 2017 Merger $ 41,375 $ 12,872 $ — Amortization related to other intangible assets 1,209 500 500 Amortization of intangibles $ 42,584 $ 13,372 $ 500 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 17.9 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 December 31, 2018 , management anticipates that the composition and amount of amortization associated with intangible assets will be $42.7 million for each of the years 2019 through 2021, $42.6 million in 2022, and $42.3 million in 2023. 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. See Note 2 for accounting policies regarding goodwill and other intangible assets.

Accrued Payroll and Purchased T

Accrued Payroll and Purchased Transportation and Accrued Liabilities	12 Months Ended
	Dec. 31, 2018
Accrued Liabilities [Abstract]
Accrued Liabilities	Accrued Payroll and Purchased Transportation and Accrued Liabilities The following table presents the composition of accrued payroll and purchased transportation: December 31, 2018 2017 (In thousands) Accrued payroll (1) $ 68,121 $ 58,438 Accrued purchased transportation 58,343 48,579 Accrued payroll and purchased transportation $ 126,464 $ 107,017 (1) Accrued payroll includes accruals related to the various 401(k) plans the Company offers to its employees. In order to qualify for these plans, employees must meet the minimum age requirement ( 18 – 21 years) and have completed six months to one year of service with the Company. Employees' rights to employer contributions are fully vested after five to 6 years from their date of employment. The plans offer discretionary matching contributions capped at either $1,600 annually per employee or 3% of an employee's compensation. The Company's employee benefits expense for matching contributions related to the 401(k) plans was approximately $8.7 million , $3.9 million , and $1.2 million in 2018 , 2017 , and 2016 , respectively. This expense was included in "Salaries, wages, and benefits" in the consolidated income statements. As of December 31, 2018 and 2017 , the balance included $6.4 million and $6.8 million , respectively, in respect to matching contributions for the 401(k) plans. The following table presents the composition of accrued liabilities: December 31, 2018 2017 (In thousands) Accrued legal (1) 90,789 121,453 Other 60,711 64,926 Accrued liabilities $ 151,500 $ 186,379 (1) See Note 20 for further details regarding the Company's legal accruals.

Claims Accruals

Claims Accruals	12 Months Ended
	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Abstract]
Claims Accruals	Claims Accruals Claims accruals represent the uninsured portion of outstanding claims at year-end. The current portion reflects the amount of claims expected to be paid in the following year. The Company's insurance program for workers' compensation, auto and collision liability, physical damage, independent contractor claims, and cargo damage involves self-insurance with varying risk retention levels. Claims accruals were comprised of the following: December 31, 2018 2017 (In thousands) Auto reserves $ 222,004 $ 204,400 Workers’ compensation reserves 120,522 126,563 Independent contractor claims reserves 12,170 15,236 Cargo damage reserves 2,998 4,047 Employee medical reserves 3,677 3,183 Claims accruals 361,371 353,429 Less: current portion of claims accruals (160,044 ) (147,285 ) Claims accruals, less current portion $ 201,327 $ 206,144 Self Insurance The Company is insured against auto liability ("AL") claims under a primary self-insured retention ("SIR") policy. Knight's AL claims have SIRs ranging from $1.0 million to $3.0 million per occurrence depending on the policy period. Swift AL claims have $250.0 million of coverage per occurrence ( $350.0 million aggregated limits through October 31, 2016), subject to a $10.0 million SIR per-occurrence. For the policy period March 1, 2018 to March 1, 2019, the Knight SIR is $1.0 million with additional responsibility up to $1.6 million per occurrence within its primary limit and applicable aggregate limits. For the policy period March 1, 2017 to March 1, 2018, the Knight SIR was $1.0 million , with additional responsibility up to $1.6 million per occurrence within its primary limit and applicable aggregate limits. For the policy period March 1, 2016 to March 1, 2017, the Knight SIR was $2.5 million with no additional aggregate limits or deductibles within the primary AL policy. Knight secured excess liability coverage up to $250.0 million per occurrence ( $130.0 million through October 31, 2018). Knight also carries a $2.5 million aggregate deductible for any loss or losses within the excess coverage layer. 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. The Knight self-retention level has a maximum of $1.0 million per occurrence. Additionally, through Knight, the Company maintains primary and excess coverage for employee medical expenses and hospitalization, with self-insured retention of $0.3 million per claimant. Since January 1, 2015, Swift has been fully insured on its medical benefits, subject to contributed premiums. See Note 2 for accounting policy regarding the Company's claims accruals.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following table presents the Company's income tax expense: 2018 2017 2016 (In thousands) Current expense: Federal $ 44,357 $ 4,868 $ 43,638 State 22,300 8,337 8,500 Foreign 3,124 133 — 69,781 13,338 52,138 Deferred expense (benefit): Federal 59,508 (323,326 ) 6,789 State 1,639 17,731 (1,335 ) Foreign 461 541 — 61,608 (305,054 ) 5,454 Income tax expense (benefit) $ 131,389 $ (291,716 ) $ 57,592 Rate Reconciliation — Expected tax expense is computed by applying the US federal corporate income tax rate of 21.0% to earnings before income taxes for 2018, and 35.0% for 2017 and 2016. Actual tax expense differs from expected tax expense as follows: 2018 2017 2016 (In thousands) Computed "expected" tax expense $ 117,478 $ 67,798 $ 53,490 Increase (decrease) in income taxes resulting from: State income taxes, net of federal income tax benefit 19,256 4,871 4,657 Statutory rate change effect on deferred taxes 452 (367,000 ) — Other (5,797 ) 2,615 (555 ) Income tax expense (benefit) $ 131,389 $ (291,716 ) $ 57,592 Deferred Income Taxes — The components of the net deferred tax asset (liability) included in "Deferred tax liabilities" in the consolidated balance sheets were: December 31, 2018 2017 (In thousands) Deferred tax assets: Claims accrual $ 79,675 $ 70,564 Allowance for doubtful accounts 5,333 5,117 Amortization of stock options 5,325 4,717 Accrued liabilities 27,692 37,654 Vacation accrual 3,499 3,585 Other 8,759 7,227 Total deferred tax assets 130,283 128,864 Valuation allowance — — Total deferred tax assets, net 130,283 128,864 Deferred tax liabilities: Property and equipment, principally due to differences in depreciation (503,570 ) (429,917 ) Prepaid taxes, licenses, and permits deducted for tax purposes (10,933 ) (10,217 ) Intangible assets (354,944 ) (365,564 ) Other (374 ) (2,243 ) Deferred tax liabilities (869,821 ) (807,941 ) Deferred income taxes $ (739,538 ) $ (679,077 ) Valuation Allowance — As of December 31, 2018 , the Company had a federal net operating loss carryforward with estimated tax effects of $0.2 million . The federal net operating loss will expire at various times between 2030 and 2032 . As of December 31, 2018 , the Company had state income tax credit carryforwards for which a deferred tax asset was recorded in the amount of $1.3 million and expires in the year 2022. 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 asserts that it is more like ly than not that the results of future operations will generate sufficient taxable income to realize the deferred tax assets. All other deferred tax assets are expected to be realized and utilized by continued profitability in future periods. Cumulative Undistributed Foreign Earnings — As of December 31, 2018 , foreign withholding taxes have not been provided on approximately $75.0 million of cumulative undistributed earnings of foreign subsidiaries. The earnings are considered to be permanently reinvested outside the US. As such, the Company is not required to provide withholding taxes on these earnings until they are repatriated in the form of dividends or otherwise. Unrecognized Tax Benefits — The Company's unrecognized tax benefits as of December 31, 2018 would favorably impact the Company's effective tax rate if subsequently recognized. See Note 2 for accounting policy related to the Company's income taxes. A reconciliation of the beginning and ending amounts of unrecognized tax benefits for 2018, 2017, and 2016 is as follows: 2018 2017 2016 (In thousands) Unrecognized tax benefits at beginning of year $ 7,096 $ 729 $ — Increases for tax positions taken prior to beginning of year 1,056 5,432 729 Increases for tax positions taken in the current year — 935 — Decreases for tax positions taken prior to beginning of year (729 ) — — Unrecognized tax benefits at end of year $ 7,423 $ 7,096 $ 729 Increases for tax positions related primarily to the impact of refunds from federal amended returns for tax years 2012, 2015, and 2016. Decreases in tax positions related primarily to a settlement of federal tax credit claims with the relevant taxing authority. The Company does not anticipate a decrease of unrecognized tax benefits during the next twelve months. Interest and Penalties — Accrued interest and penalties as of December 31, 2018 were approximately $1.4 million . The Company had $0.3 million and no interest and penalties accrued as of December 31, 2017 and 2016 , respectively. Tax Examinations — The Company is currently under examination by the IRS for the 2014 tax year and management does not expect any adjustments that would have a material impact on the Company's effective tax rate. Certain of the Company's subsidiaries are also currently under examination by various state jurisdictions for tax years ranging from 2011 to 2017 . 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 2013 remain subject to examination. Regulatory Developments — On December 22, 2017, the US government enacted significant changes to US tax law following the passage and signing of H.R.1, "An Act to Provide for Reconciliation Pursuant to Titles II and V of the Concurrent Resolution on the Budget for Fiscal Year 2018" (previously known as "The Tax Cuts and Jobs Act" and hereafter "the Act"). See Note 3 for details.

Accounts Receivable Securitizat

Accounts Receivable Securitization	12 Months Ended
	Dec. 31, 2018
Transfers and Servicing of Financial Assets [Abstract]
Accounts Receivable Securitization	Accounts Receivable Securitization On July 11, 2018, Swift Receivables Company II, LLC ("SRCII") , a wholly-owned subsidiary of the Company, entered into the 2018 RSA, which further amended the 2015 RSA. The parties to the 2018 RSA are SRCII as the seller, Swift Transportation Services, LLC as the servicer, the various conduit purchasers, the various related committed purchasers, the various purchaser agents, the various letters of credit participants, and PNC Bank, National Association as the issuing bank for letters of credit and as administrator. Pursuant to the related purchase and sale agreement and together with the 2018 RSA, the Company's receivable originator subsidiaries sell, on a revolving basis, undivided interests in all of their eligible accounts receivable to SRCII. In turn, SRCII sells a variable percentage ownership interest in the eligible accounts receivable to the various purchasers. The 2018 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 December 31, 2018 . 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 differences between the 2018 RSA and 2015 RSA: 2018 RSA 2015 RSA (Dollars in thousands) Effective July 11, 2018 December 10, 2015 Final maturity date July 9, 2021 January 10, 2019 Borrowing capacity $325,000 $400,000 Accordion option (1) $175,000 $75,000 Unused commitment fee rate (2) 20 to 40 basis points 35 basis points Program fees on outstanding balances (3) one month LIBOR + 80 to 100 basis points one-month LIBOR + 90 basis points (1) The accordion option increases the maximum borrowing capacity, subject to participation by the purchasers. (2) The 2018 RSA commitment fee rate is based on the percentage of the maximum borrowing capacity utilized. (3) The 2018 RSA program fee is based on the Company's consolidated total net leverage ratio. The 2018 RSA and 2015 RSA are secured borrowings that are collateralized by the Company's eligible receivables, for which the Company is the servicing agent. The Company's eligible receivables are included in "Trade receivables, net of allowance for doubtful accounts" in the consolidated balance sheets. As of December 31, 2018 , the Company's eligible receivables generally have high credit quality, as determined by the obligor's corporate credit rating. Availability under the 2018 RSA and 2015 RSA is calculated as follows: 2018 RSA 2015 RSA December 31, December 31, (In thousands) Borrowing base, based on eligible receivables $ 325,000 $ 317,600 Less: outstanding borrowings (1) (240,000 ) (305,000 ) Less: outstanding letters of credit (70,900 ) — Availability under accounts receivable securitization facilities $ 14,100 $ 12,600 (1) Outstanding borrowings are included in "Accounts receivable securitization" in the consolidated balance sheets. Interest accrued on the aggregate principal balance at a rate of 3.2% and 2.1% , as of December 31, 2018 and 2017 , respectively. Program fees and unused commitment fees are recorded in "Interest expense" in the consolidated income statements. The Company's accounts receivable securitization incurred program fees of $8.1 million in 2018 and $2.2 million in 2017 . Refer to Note 24 for information regarding the fair value of the 2018 RSA and the 2015 RSA.

Debt And Financing

Debt And Financing	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt And Financing	Debt and Financing Other than the Company's accounts receivable securitization as discussed in Note 16 and its outstanding capital lease obligations as discussed in Note 18 , the Company's long-term debt consisted of the following: December 31, 2018 2017 (In thousands) Term Loan, due October 2020, net (1) (2) $ 364,590 $ 364,355 Other long-term debt, including current portion 421 446 Total long-term debt, including current portion 365,011 364,801 Less: current portion of long-term debt (421 ) (30 ) Long-term debt, less current portion $ 364,590 $ 364,771 December 31, 2018 2017 (In thousands) Total long-term debt, including current portion $ 365,011 $ 364,801 Revolver, due October 2022 (1) (3) 195,000 125,000 Long-term debt, including revolving line of credit $ 560,011 $ 489,801 (1) Refer to Note 24 for information regarding the fair value of debt. (2) Net of $0.4 million and $0.6 million deferred loan costs at December 31, 2018 and 2017 , respectively. (3) The Company also had outstanding letters of credit under the Revolver, primarily related to workers' compensation and self-insurance liabilities of $36.6 million and $153.6 million at December 31, 2018 and 2017 , respectively. Credit Agreements 2017 Debt Agreement — On September 29, 2017 , Knight-Swift entered into the $1.2 billion 2017 Debt Agreement (which is an unsecured credit facility), with a group of banks, replacing Swift's previous secured 2015 Debt Agreement, and Knight's unsecured 2013 Debt Agreement. The 2017 Debt Agreement includes an $800.0 million Revolver maturing October 2022 , $85.0 million of which was drawn at closing, and a $400.0 million Term Loan maturing October 2020 . There are no scheduled principal payments on the Term Loan until its maturity. The 2015 Debt Agreement included a $600.0 million revolving line of credit maturing July 2020 ( $35.0 million outstanding as of the closing of the 2017 Debt Agreement) and a $680.0 million Term Loan A ( $450.0 million face value outstanding as of closing). Additionally, prior to the 2017 Merger, the 2013 Debt Agreement included a $300.0 million Knight Revolver maturing August 2019 , with no balance outstanding as of the closing of the 2017 Debt Agreement. Upon closing of the 2017 Debt Agreement, proceeds from the $400.0 million Term Loan, $85.0 million drawn from the Revolver, and $3.4 million cash on hand were used to pay off the then-outstanding balances and accrued interest and fees under the 2015 Debt Agreement, as well as certain transaction fees and expenses associated with the 2017 Debt Agreement. Under the 2017 Debt Agreement, the interest rate on the Revolver and the Term Loan is subject to a leverage-based pricing grid and equaled the LIBOR rate plus 1.125% at closing. The following table presents the key terms of the 2017 Debt Agreement: Term Loan Revolver (2) 2017 Debt Agreement Terms: (Dollars in thousands) Maximum borrowing capacity $400,000 $800,000 Final maturity date October 2, 2020 October 3, 2022 Interest rate base LIBOR LIBOR Interest rate minimum margin (1) 0.88% 0.88% Interest rate maximum margin (1) 1.50% 1.50% Minimum principal payment — amount $— $— Minimum principal payment — frequency Once Once Minimum principal payment — commencement date October 2, October 3, (1) The interest rate margin for the Term Loan and Revolver is based on the Company's consolidated leverage ratio. As of December 31, 2018 , interest accrued at 3.522% on the Term Loan and 3.448% on the Revolver. As of December 31, 2017 interested accrued at 2.694% on the Term Loan and 2.687% on the Revolver. (2) The commitment fee for the unused portion of the Revolver is based on the Company's consolidated leverage ratio, and ranges from 0.07% to 0.20% . As of December 31, 2018 , commitment fees on the unused portion of the Revolver accrued at 0.100% and outstanding letter of credit fees accrued at 1.000% . As of December 31, 2017 , commitment fees on the unused portion of the Revolver accrued at 0.125% and outstanding letter of credit fees accrued at 1.125% . Pursuant to the 2017 Debt Agreement, the Revolver and the Term Loan contain certain financial covenants with respect to a maximum net leverage ratio and a minimum consolidated interest coverage ratio. The 2017 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 2017 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 2017 Debt Agreement may be accelerated, and the lenders' commitments may be terminated. The 2017 Debt Agreement contains certain usual and customary restrictions and covenants relating to, among other things, dividends (which would be restricted only if a default or event of default had occurred and was continuing or would result therefrom), liens, affiliate transactions, and other indebtedness. As of December 31, 2018 and 2017, the Company was in compliance with the debt covenants that the 2017 Debt Agreement was subject to. Borrowings under the 2017 Debt Agreement are guaranteed by Knight-Swift Transportation Holdings Inc., Swift Transportation Company, Interstate Equipment Leasing, LLC, Knight Transportation, Inc. and the Company's domestic subsidiaries (other than its captive insurance subsidiaries, driving academy subsidiary, and bankruptcy-remote special purpose subsidiary). Knight Revolver — Prior to the closing of the 2017 Debt Agreement, the 2013 Debt Agreement included the $300.0 million Knight Revolver, which permitted revolving borrowings and letters of credit. The scheduled maturity of the Knight Revolver was August 1, 2019 , which was accelerated to December 31, 2017 in connection with the closing of the 2017 Merger. Knight incurred interest on borrowings under the Knight Revolver at either the prime rate or LIBOR plus 0.625% , determined by Knight at the time of borrowing. Excluding commitment fees incurred for the unused portion of the Knight Revolver, the weighted average variable annual percentage rate for 2017 was 1.40% . The Knight Revolver was subject to commitment fees for any unused portion at a rate of 0.8% . See Note 24 for fair value disclosures regarding the Company's debt instruments.

Leases

Leases	12 Months Ended
	Dec. 31, 2018
Leases [Abstract]
Leases	Leases The Company finances a portion of its revenue equipment under capital and operating leases and certain terminals under operating leases. Capital Leases (as Lessee) — The Company's capital leases are typically structured with balloon payments at the end of the lease term equal to the residual value the Company is contracted to receive from certain equipment manufacturers upon sale or trade back to the manufacturers. If the Company does not receive proceeds of the contracted residual value from the manufacturer, the Company is still obligated to make the balloon payment at the end of the lease term. Certain leases contain renewal or fixed price purchase options. The present value of obligations under capital leases is included under "Capital lease obligations and long-term debt – current portion" and "Capital lease obligations – less current portion" in the consolidated balance sheets. As of December 31, 2018 , the leases were collateralized by revenue equipment with a cost of $154.3 million and accumulated amortization of $34.2 million . As of December 31, 2017 , the leases were collateralized by revenue equipment with a cost of $173.7 million and accumulated amortization of $9.4 million . Knight had no capital leases as of December 31, 2016 , therefore no revenue equipment was held as collateral during that period. Amortization of the equipment under capital leases is included in "Depreciation and amortization of property and equipment" in the Company's consolidated income statements. Operating Leases (as Lessee) — Operating leases generally include tractors, trailers, chassis, and facilities. Substantially all lease agreements for revenue equipment have fixed payment terms based on the passage of time. The tractor lease agreements generally stipulate maximum miles and provide for mileage penalties for excess miles. These leases generally run for a period of three to five years for tractors and five to seven years for trailers. Operating and Capital Leases (as Lessee) — As of December 31, 2018 , annual future minimum lease payments for all noncancelable leases were: Operating Capital (In thousands) 2019 $ 123,380 $ 61,285 2020 79,088 15,843 2021 42,441 30,845 2022 24,693 18,528 2023 11,728 1,347 Thereafter 25,403 9,572 Future minimum lease payments $ 306,733 $ 137,420 Less: amounts representing interest (7,921 ) Present value of minimum lease payments 129,499 Less: current portion (58,251 ) Capital lease obligations – less current portion $ 71,248 Operating Leases (as Lessor) — The Company's wholly-owned financing subsidiaries lease revenue equipment to the Company's independent contractors under operating leases. Additionally, the Company periodically leases out facilities for use by third-parties. Annual future minimum lease payments receivable under operating leases for the periods noted below were: (In thousands) 2019 $ 54,080 2020 37,694 2021 22,991 2022 8,343 2023 13 Thereafter — Future minimum lease payments receivable $ 123,121 Lease classification is determined based on minimum rental payments per the agreement, including residual value guarantees, when applicable, as well as receivables due to the Company upon default or cross-default. When independent-contractors default on their leases, the Company typically re-leases the equipment to other independent-contractors. As such, future minimum lease payments reflect original leases and re-leases.

Purchase Commitments

Purchase Commitments	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Purchase Commitments	Purchase Commitments As of December 31, 2018 , the Company had outstanding commitments to acquire revenue equipment of $705.0 million in 2019 ( $662.7 million of which were tractor commitments) and none thereafter. These purchases may be financed through any combination of operating leases, capital leases, debt, proceeds from sales of existing equipment, and cash flows from operations. As of December 31, 2018 , the Company had outstanding purchase commitments to acquire facilities and non-revenue equipment of $5.8 million in 2019 , $0.6 million in the two-year period 2020 through 2021, and none thereafter. Factors such as costs and opportunities for future terminal expansions may change the amount of such expenditures.

Contingencies and Legal Proceed

Contingencies and Legal Proceedings	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Legal Proceedings	Contingencies and Legal Proceedings Accounting Policy The Company is involved in certain claims and pending litigation primarily arising in the normal course of business. The majority of these claims relate to workers' compensation, auto collision and liability, physical damage, and cargo damage, as well as certain class action litigation in which plaintiffs allege failure to provide meal and rest breaks, unpaid wages, unauthorized deductions, and other items. The Company accrues for the uninsured portion of claims losses and the gross amount of other losses when the likelihood of the loss is probable and the amount of the loss is reasonably estimable. These accruals are based on management's best estimate within a possible range of loss. When there is no amount within the range of loss that appears to be a better estimate than any other amount, then management accrues to the low end of the range. Legal fees are expensed as incurred. When it is reasonably possible that exposure exists in excess of the related accrual (which could be no accrual), management discloses an estimate of the possible loss or range of loss, unless an estimate cannot be determined (because, among other reasons, (1) the proceedings are in various stages that do not allow for assessment; (2) damages have not been sought; (3) damages are unsupported and/or exaggerated; (4) there is uncertainty as to the outcome of pending appeals; and/or (5) there are significant factual issues to be resolved). If the likelihood of a loss is remote, the Company does not accrue for the loss. However, if the likelihood of a loss is remote, but it is at least reasonably possible that one or more future confirming events may materially change management's estimate within twelve months from the date of the financial statements, management discloses an estimate of the possible loss or range of loss, unless an estimate cannot be determined. 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 consolidated balance sheets. The Company has recorded an aggregate accrual of approximately $90.8 million and $121.5 million relating to the Company's outstanding legal proceedings as of December 31, 2018 and 2017 , respectively. 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 Washington Overtime Class Actions The plaintiffs allege one or more of the following, pertaining to Washington state-based driving associates: that Swift 1) failed to pay minimum wage; 2) failed to pay overtime; 3) failed to pay all wages due at established pay periods; 4) failed to provide proper meal and rest periods; 5) failed to provide accurate wage statements; and 6) unlawfully deducted from employee wages. The plaintiffs seek unpaid wages, exemplary damages, interest, other costs, and attorneys’ fees. Plaintiff(s) Defendant(s) Date instituted Court or agency currently pending in Troy Slack (1) Swift Transportation Company of Arizona, LLC and Swift Transportation Corporation September 9, 2011 United States District Court for the Western District of Washington Julie Hedglin (1) Swift Transportation Company of Arizona, LLC and Swift Transportation Corporation January 14, 2016 United States District Court for the Western District of Washington Recent Developments and Current Status The parties in the Slack matter have reached a final settlement. Additionally, the parties in the Hedglin matter have reached a final settlement. The likelihood that a loss has been incurred for the Slack and Hedglin matters is probable and estimable, and the loss has accordingly been accrued. 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 The parties have reached a tentative settlement of the matter. As such, the likelihood that a loss has been incurred is probable and estimable, and the loss has accordingly been accrued. (1) Individually and on behalf of all others similarly situated. INDEPENDENT CONTRACTOR MATTERS Ninth Circuit Independent Contractors Misclassification Class Action The putative class alleges that Swift misclassified independent contractors as independent contractors, instead of employees, in violation of the FLSA 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 2017, the district court issued an order finding that the plaintiffs had signed contracts of employment and thus the case could properly proceed in court, instead of arbitration. In February 2019, the parties reached a tentative settlement pending approval by the court. Based on the above, the likelihood that a loss has been incurred is probable and estimable, and the loss has accordingly been accrued. Utah Collective and Individual Arbitration The plaintiffs allege that the Central Parties (defined below) misclassified independent contractors as independent contractors, instead of employees, in violation of the FLSA and various state laws. 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 Gabriel Ciluffo, Kevin Shire, and Bryan Ratterree (1) Central Refrigerated Service, Inc., Central Leasing, Inc., Jon Isaacson, and Jerry Moyes (the "Central Parties"), as well as Swift Transportation Company June 1, 2012 American Arbitration Association Recent Developments and Current Status In October 2016, the arbitrator ruled that approximately 1,300 Central Refrigerated Service, Inc. drivers should have been classified as employees, not independent contractors. The arbitrator ruled that damages could ultimately be assessed in a collective proceeding and denied Swift's motion to decertify the collective proceeding. On April 14, 2017, the parties reached a settlement of the matter. On April 3, 2018, the court granted final approval of the settlement and the Company paid the settlement in the second quarter of 2018. (1) Individually and on behalf of all others similarly situated.

Share Repurchase Plans

Share Repurchase Plans	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Share Repurchase Plans	Share Repurchase Plans In 2011, Knight's board of directors unanimously authorized the repurchase of up to 10.0 million shares of Knight common stock (the "Knight Repurchase Plan"). There were 1.6 million share repurchases under the Knight Repurchase Plan in 2016. There were no repurchases in 2017. In connection with the 2017 Merger, the Knight Repurchase Plan was terminated. In February 2016, Swift's board of directors authorized the repurchase of up to $150.0 million of Swift common stock (the "Swift Repurchase Plan"). Following the 2017 Merger, the Swift Repurchase Plan remained in effect. The Company did not repurchase any shares of its common stock under the Swift Repurchase Plan from September 9, 2017 through December 31, 2017. On June 1, 2018, the Board approved the repurchase of up to $250.0 million of the Company's outstanding common stock (the "Knight-Swift Repurchase Plan"). With the adoption of the Knight-Swift Repurchase Plan, the Company terminated the Swift Repurchase Plan. When terminated, the Swift Repurchase Plan had approximately $62.9 million in remaining authorized purchases. During 2018, the Company purchased 5.9 million shares of its common stock for $179.3 million under the Knight-Swift Repurchase Plan, and as such $70.7 million in authorized purchases remained as of December 31, 2018. Refer to Note 25 for a discussion of shares repurchase transactions conducted with related parties.

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation	Stock-based Compensation 2017 Merger Impact — Refer to Note 5 for a summary of the 2017 Merger transaction. Accounting Perspective — Pursuant to the Merger Agreement, the following stock transactions occurred on September 8, 2017 (the "Merger Date"): (1) each outstanding Swift stock option fully vested as a result of the 2017 Merger, was converted into a stock option to acquire the Company's shares using a 0.72-for-one share consolidation ratio and adjusting the exercise price using the same consolidation ratio; (2) each outstanding unvested Swift restricted stock award (except for the awards granted in May 2017 that excluded acceleration of vesting related to mergers within the award notices) fully vested as a result of the 2017 Merger, and was converted into the Company's Class A common stock, using the 0.72-for-one share consolidation ratio; (3) each outstanding unvested Swift restricted stock unit (except for the awards granted in May 2017 that excluded acceleration of vesting related to mergers within the award notices) fully vested as a result of the 2017 Merger, and was converted into the Company's Class A common stock, using the 0.72-for-one share consolidation ratio; and (4) each outstanding unvested Swift performance share unit (except for one director) fully vested as a result of the 2017 Merger, and was converted into the Company's Class A common stock, using the 0.72-for-one consolidation ratio. Except for the conversion of stock options, unvested restricted stock awards, unvested restricted stock units, and unvested performance units discussed herein, the material terms of the awards remained unchanged. Prior to the closing of the 2017 Merger, Swift had various unvested equity awards outstanding, of which the vesting was accelerated as of the Merger Date (with the exceptions noted above). In accordance with authoritative guidance on accounting for stock-based compensation, the Company revalued the awards upon the 2017 Merger closing and allocated the revised fair value between purchase consideration and continuing compensation expense, based on the ratio of service performed through the Merger Date over the total service period of the awards. The total value of Swift awards earned as of the Merger Date included as purchase consideration was $13.1 million . The revised fair value allocated to post-merger services resulted in incremental expense, which is recognized over the remaining service period of the awards. The total value of Swift awards not earned as of the Merger Date was $6.3 million , which is being expensed over the remaining future vesting period. Of this amount, $1.0 million was recorded within "Salaries, wages, and benefits" in the 2017 consolidated income statements. Refer to Note 5 to the consolidated financial statements for further information regarding the 2017 Merger. Legal Perspective — Pursuant to the Merger Agreement, the following stock transactions occurred on the Merger Date: (1) each outstanding vested and unvested Knight stock option was assumed by the Company and automatically converted into a stock option to acquire an equal number of Company shares; (2) each outstanding vested and unvested Knight restricted stock unit was assumed by the Company and automatically converted into a restricted stock unit award of the Company; and (3) each outstanding vested and unvested Knight performance unit was assumed by the Company and automatically converted into a performance unit award of the Company. Except for the conversion of stock options, restricted stock awards, restricted stock unit awards, and performance unit awards discussed herein, the material terms of the awards remained unchanged. Certain of the Knight performance unit awards vested upon the consummation of the 2017 Merger, as described below. Compensatory Stock Plans Before the 2017 Merger, Knight and Swift granted stock-based awards under their respective stock-based compensation plans, discussed below. 2014 Stock Plan — Currently, the 2014 Stock Plan, as amended and restated, is the combined company’s only compensatory stock-based incentive plan. The previous 2014 stock plan replaced Swift's 2007 Omnibus Incentive Plan when it was adopted by Swift's board of directors in March 2014 and then approved by the Swift stockholders in May 2014. The previous 2014 stock plan was amended and restated to rename the plan and for other administrative changes relating to the 2017 Merger. The terms of the 2014 Stock Plan, as amended and restated, remain substantially the same as the previous 2014 stock plan. The 2014 Stock Plan, as amended and restated, permits the payment of cash incentive compensation and authorizes the granting of stock options, stock appreciation rights, restricted stock and restricted stock units, performance shares and performance units, cash-based awards, and stock-based awards to the Company's employees and non-employee directors. As of December 31, 2018 , the aggregate number of shares remaining available under the 2014 Stock Plan was approximately 2.2 million . Legacy Plans — In connection with the 2017 Merger, the registered securities under the Knight Amended and Restated 2003 Stock Option Plan, the Knight 2012 Equity Compensation Plan, the Knight Amended and Restated 2015 Omnibus Incentive Plan, and the Swift 2007 Omnibus Incentive Plan (collectively, the "Legacy Plans") were deregistered. As such, no future awards may be granted under these Legacy Plans. Outstanding awards granted under the Legacy Plans were assumed by the combined company and continue to be governed by such Legacy Plans until such awards have been exercised, forfeited, canceled, or have otherwise expired or terminated. See Note 2 regarding the Company's accounting policy for stock-based compensation. Stock-based Compensation Expense Stock-based compensation expense, net of forfeitures, which is included in "Salaries, wages, and benefits" in the consolidated income statements is comprised of the following: 2018 2017 2016 (In thousands) Stock options $ 1,678 $ 1,788 $ 1,734 Restricted stock units and restricted stock awards 8,019 4,004 1,506 Performance units 1,791 450 801 Stock-based compensation expense – equity awards $ 11,488 $ 6,242 $ 4,041 Stock-based compensation expense – liability awards (1) 899 148 — Total stock-based compensation expense, net of forfeitures 12,387 6,390 4,041 Income tax benefit $ 3,097 $ 2,415 $ 1,515 (1) Includes awards granted to executive management in November 2017 and November 2018 that ultimately settle in cash upon fulfilling a requisite service period (for restricted stock units) and fulfilling a requisite service period and achieving performance targets (for performance units). Unrecognized Stock-based Compensation Expense The following table presents the total unrecognized stock-based compensation expense and the expected weighted average period over which these expenses will be recognized: December 31, 2018 Expense Weighted Average Period (In thousands) (In years) Equity awards – Stock options $ 2,092 1.4 Equity awards – Restricted stock units and restricted stock awards 23,803 2.2 Equity awards – Performance units 3,763 2.8 Liability awards – Restricted stock units and performance units 3,067 2.4 Total unrecognized stock-based compensation expense $ 32,725 2.3 Stock Award Grants 2018 2017 2016 Stock options — 497,421 569,480 Restricted stock units and restricted stock awards 420,014 266,958 17,000 Performance units 106,785 44,244 177,741 Equity awards granted 526,799 808,623 764,221 Liability awards granted (1) (2) 91,268 77,620 — Total stock awards granted 618,067 886,243 764,221 (1) Includes 54,761 and 46,572 performance units in 2018 and 2017 , respectively. (2) Includes 36,507 and 31,048 restricted stock units in 2018 and 2017 , respectively. Stock Options Stock options are the contingent right of award holders to purchase shares of the Company's common stock at a stated price for a limited time. The exercise price of options granted equals the fair value of the Company's common stock determined by the closing price of the Company's common stock quoted on the NYSE on the grant date. Most stock options granted by the Company cannot be exercised until at least one year after the grant date and have a five to ten -year contractual term. Stock options are forfeited upon termination of employment for reasons other than death, disability, or retirement. A summary of 2018 stock option activity follows: Stock options outstanding: Shares Under Option Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (1) (In years) (In thousands) Stock options outstanding at December 31, 2017 1,959,291 $ 25.48 3.2 $ 35,779 Granted — — Exercised (2) (533,226 ) 20.56 Expired (26,163 ) 28.72 Forfeited (78,297 ) 30.17 Stock options outstanding at December 31, 2018 1,321,605 $ 27.13 2.6 $ 2,690 Aggregate number of stock options expected to vest at a future date as of December 31, 2018 558,184 $ 29.71 2.7 $ 160 Exercisable at December 31, 2018 739,264 $ 25.02 2.6 $ 2,527 (1) The aggregate intrinsic value was computed using the closing share price on December 31, 2018 of $25.07 and on December 29, 2017 of $43.72 , as applicable. (2) Includes 3,044 swapped shares which were excluded from the "Common stock issued to employees" activity on the Consolidated Statements of Stockholders' Equity. The fair value of each stock option grant is estimated on the grant date using the Black-Scholes option-valuation model. The following table presents the weighted average assumptions used in the fair value computation: Stock option fair value assumptions: 2017 2016 Dividend yield (1) 0.72% 0.99% Risk-free rate of return (2) 1.49% 0.90% Expected volatility (3) 27.95% 27.91% Expected term (in years) (4) 3.2 2.7 Weighted average fair value of stock options granted $6.78 $4.28 (1) The dividend yield assumption is based on Knight's historical experience and anticipated future dividend payouts. (2) The risk-free interest rate assumption is based on the US Treasury securities at a constant maturity with a maturity period that most closely resembles the expected term of the stock option award. (3) Expected volatility of the Company's common stock is determined based on Knight's historical data. (4) The expected term of employee stock options represents the weighted-average period the stock options are expected to remain outstanding and was determined based on an analysis of historical exercise behavior. The following table summarizes stock option exercise information for the years presented: Stock option exercises 2018 2017 2016 (In thousands, except share data) Number of stock options exercised 533,226 589,020 708,244 Intrinsic value of stock options exercised $ 11,745 $ 8,792 $ 7,100 Cash received upon exercise of stock options $ 10,815 $ 13,159 $ 13,188 Income tax benefit $ 1,685 $ 1,833 $ 1,847 The following table is a rollforward of the Company's unvested stock options: Unvested stock options: Shares Weighted Average Fair Value Unvested stock options at December 31, 2017 1,040,697 $ 5.49 Granted — — Vested (380,059 ) 5.14 Forfeited (78,297 ) 5.76 Unvested stock options at December 31, 2018 582,341 $ 5.69 The total fair value of the shares vested during 2018 , 2017 , and 2016 was $2.0 million , $1.7 million , and $1.4 million , respectively. Restricted Stock Units A restricted stock unit represents a right to receive a common share of stock when the unit vests. Restricted stock unit recipients do not have voting rights with respect to the shares underlying unvested awards. Employees forfeit their units if their employment terminates before the vesting date. The following table is a rollforward of unvested restricted stock units, including restricted stock units classified as equity and those classified as liabilities: Unvested restricted stock units: Number of Awards Weighted Average Fair Value (1) Unvested restricted stock units at December 31, 2017 979,717 $ 26.59 Granted 456,521 38.07 Vested (2) (193,502 ) 24.43 Forfeited (72,762 ) 37.98 Unvested restricted stock units at December 31, 2018 1,169,974 $ 30.14 (1) The fair value of each restricted stock unit is based on the closing market price on the grant date. (2) Includes 53,274 of shares withheld for taxes which were excluded from the "Common stock issued to employees" activity on the Consolidated Statements of Stockholders' Equity. Performance Units The Company issues performance units to selected key employees, that may be earned based on achieving performance targets approved by the compensation committee annually. The initial award is subject to an adjustment determined by the Company's performance achieved over a three-year performance period when compared to the objective performance standards adopted by the compensation committee. Furthermore, the performance units have additional service requirements subsequent to the achievement of the performance targets. Performance units do not earn dividend equivalents. Performance units granted prior to the 2017 Merger were accelerated on September 8, 2017, the 2017 Merger date, pursuant to the terms of the award agreements. On the 2017 Merger date, awards granted in 2014, 2015, and 2016 were accelerated, but only the performance measurement period for the 2014 award was complete allowing for the final award to be expensed and paid out. The performance period for the 2015 and 2016 awards ended December 31, 2017. The performance criteria were not met based on the performance period results ended December 31, 2017, therefore, no expense was recorded, and no payout was made related to the 2015 or 2016 awards. The following table is a rollforward of unvested performance units, including performance units classified as equity and those classified as liabilities: Unvested performance units: Shares Weighted Average Fair Value Unvested performance units at December 31, 2017 147,633 $ 35.34 Granted 161,546 $ 34.34 Shares earned above target — $ — Vested — $ — Forfeited — $ — Unvested performance units at December 31, 2018 (1) 309,179 $ 29.50 (1) The performance measurement period for performance units granted in 2017 is January 1, 2018 to December 31, 2020 (three full calendar years). These awards will vest one month following the expiration of the performance measurement period. The performance measurement period for performance units granted in 2018 is January 1, 2019 to December 31, 2021 (three full calendar years). These awards will vest one month following the expiration of the performance measurement period. The following table presents the weighted average assumptions used in the fair value computation for performance units, including performance units classified as equity and those classified as liabilities: Performance unit fair value assumptions: 2018 2017 2016 Dividend yield (1) 0.81 % 0.59 % 0.99 % Expected volatility (2) 32.30 % 31.28 % 27.95 % Average peer volatility (2) 28.61 % 28.45 % 34.37 % Average peer correlation coefficient (3) 0.58 0.60 0.60 Risk-free interest rate (4) 2.80 % 1.88 % 0.89 % Expected term (in years) (5) 3.1 3.1 2.8 Weighted-average fair value of performance units granted $ 34.34 $ 40.81 $ 23.89 (1) The dividend yield, used to project stock price to the end of the performance period, is based on the Knight's historical experience and future expectation of dividend payouts. Total stockholder return is determined assuming that dividends are reinvested in the issuing entity over the performance period, which is mathematically equivalent to utilizing a 0% dividend yield. (2) Management (or peer company) estimated volatility using Knight's (or peer company's) historical share price performance over the remaining performance period as of the grant date. (3) The correlation coefficients are used to model the way in which each entity tends to move in relation to each other; the correlation assumptions were developed using the same stock price data as the volatility assumptions. (4) The risk-free interest rate assumption is based on US Treasury securities at a constant maturity with a maturity period that most closely resembles the expected term of the performance award. (5) Since the Monte Carlo Simulation valuation is an open form model that uses an expected life commensurate with the performance period, the expected life of the performance units was assumed to be the period from the grant date to the end of the performance period. Non-compensatory Stock Plan: ESPP In 2012, Swift's board of directors adopted, and its stockholders approved, the Swift Transportation Company 2012 ESPP (the "2012 ESPP"). The 2012 ESPP continues to be administered by the Company following the 2017 Merger, is intended to qualify under Section 423 of the Internal Revenue Code, and is considered noncompensatory. Pursuant to the 2012 ESPP, the Company is authorized to issue up to 1.4 million shares of its common stock to eligible employees who participate in the plan. Employees are eligible to participate in the 2012 ESPP following at least 90 days of employment with the Company or any of its participating subsidiaries. Under the terms of the 2012 ESPP, eligible employees may elect to purchase common stock through payroll deductions, not to exceed 15% of their gross cash compensation. The purchase price of the common stock is 95% of the common stock's fair market value quoted on the NYSE on the last trading day of each offering period. There are four three -month offering periods corresponding to the calendar quarters. Each eligible employee is restricted to purchasing a maximum of $6,250 of common stock during an offering period, determined by the fair market value of the common stock as of the first day of the offering period, and $25,000 of common stock during a calendar year. Officers or employees who own 5% or more of the total voting power or value of common stock are restricted from participating in the 2012 ESPP. The 2012 ESPP was amended and restated in January 2018 to be a Knight-Swift plan, thus permitting Knight employees to participate in the plan in addition to Swift employees. The terms and definitions of the amended and restated 2012 ESPP remain substantially the same as the original 2012 ESPP. In 2018 , the Company issued approximately 49,000 shares under the 2012 ESPP at an average discounted price per share of $37.53 . As of December 31, 2018 , the Company is authorized to issue an additional 1.2 million shares under the 2012 ESPP.

Weighted Average Shares Outstan

Weighted Average Shares Outstanding	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Weighted Average Shares Outstanding	Weighted Average Shares Outstanding Basic and diluted earnings per share, as presented in the consolidated income statements, 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: December 31, 2018 2017 2016 (In thousands) Basic weighted average common shares outstanding 177,018 110,657 80,362 Dilutive effect of equity awards 981 1,040 866 Diluted weighted average common shares outstanding 177,999 111,697 81,228 Anti-dilutive shares excluded from diluted earnings per share (1) 47 98 886 (1) Shares were excluded from the dilutive-effect calculation because the outstanding awards' exercise prices were greater than the average market price the Company's common stock (for 2018 and 2017) and Knight's common stock (for 2016).

Fair Value Measurement

Fair Value Measurement	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurement	Fair Value Measurement ASC 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 December 31, 2018 and 2017 , the amounts that will actually be realized or paid at settlement or maturity of the instruments in the future could be significantly different. The tables below exclude certain financial instruments. The excluded financial instruments are as follows: cash and cash equivalents, restricted cash included in "Cash and cash equivalents – restricted", net accounts receivable, income tax refund receivable, and accounts payable. The estimated fair value of these financial instruments approximate carrying value as they are short-term in nature. Additionally, for notes payable under revolving lines of credit, fair value approximates the carrying value due to the variable interest rate. For capital leases, the carrying value approximates the fair value as the Company's capital leases are structured to amortize in a manner similar to the depreciation of the underlying assets. The table below also excludes financial instruments reported at estimated fair value on a recurring basis. See "Recurring Fair Value Measurements." All remaining balance sheet amounts excluded from the table below are not considered financial instruments subject to this disclosure. Financial Assets — The carrying amounts and estimated fair values of the Company's financial assets are included in Note 7 for restricted investments, held-to-maturity and under "Recurring Fair Value Measurements" below for other investments. Financial Liabilities — The following table presents the carrying amounts and estimated fair values of the Company's financial instruments: December 31, 2018 2017 Carrying Estimated Carrying Estimated (In thousands) Term Loan, due October 2020 (1) $ 364,590 $ 365,000 $ 364,355 $ 365,000 2018 RSA, due July 2021 (2) 239,606 240,000 — — 2015 RSA, due January 2019 — — 305,000 305,000 Revolver, due October 2022 195,000 195,000 125,000 125,000 (1) The carrying amount of the Term Loan is included in "Long-term debt – less current portion," and is net of $0.4 million and $0.6 million in deferred loan costs as of December 31, 2018 and 2017 , respectively. (2) The carrying amount of the 2018 RSA is included in "Accounts receivable securitization," and is net of $0.4 million deferred loan costs as of December 31, 2018 . The estimated fair values of the financial instruments shown in the above table as of December 31, 2018 and 2017 , 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 the Company'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 is based on quoted prices in active markets that are readily and regularly obtainable. See Note 7 for additional investments disclosures regarding restricted investments, held-to-maturity. Term Loan — The estimated fair value of the Term Loan approximates the face value. See Note 17 for additional debt disclosures. Accounts Receivable Securitization — The Company's securitization of accounts receivable consists of borrowings outstanding pursuant to the 2018 RSA as of December 31, 2018 and the 2015 RSA as of December 31, 2017 , as discussed in Note 16 . The estimated fair value of the 2018 RSA and 2015 RSA approximates the face value. Fair Value Hierarchy — ASC 820 establishes a framework for measuring fair value in accordance with GAAP and expands financial statement disclosure requirements for fair value measurements. ASC 820 further specifies a hierarchy of valuation techniques, which is based on whether the inputs into the valuation technique are observable or unobservable. The hierarchy follows: • Level 1 — Valuation techniques in which all significant inputs are quoted prices from active markets for assets or liabilities that are identical to the assets or liabilities being measured. • Level 2 — Valuation techniques in which significant inputs include quoted prices from active markets for assets or liabilities that are similar to the assets or liabilities being measured and/or quoted prices from markets that are not active for assets or liabilities that are identical or similar to the assets or liabilities being measured. Also, model-derived valuations in which all significant inputs and significant value drivers are observable in active markets are Level 2 valuation techniques. • Level 3 — Valuation techniques in which one or more significant inputs or significant value drivers are unobservable. Unobservable inputs are valuation technique inputs that reflect the Company's own assumptions about the assumptions that market participants would use in pricing an asset or liability. When available, the Company uses quoted market prices to determine the estimated fair value of an asset or liability. If quoted market prices are not available, the Company measures fair value using valuation techniques that use, when possible, current market-based or independently-sourced market parameters, such as interest rates and currency rates. The level in the fair value hierarchy within which a fair value measurement in its entirety falls is based on the lowest level input that is significant to the estimated fair value measurement in its entirety. Recurring 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 recurring basis as of December 31, 2018 and 2017 : Fair Value Measurements at Reporting Date Using Estimated Fair Value (1) Level 1 Inputs Level 2 Inputs Level 3 Inputs (In thousands) As of December 31, 2018 Money market funds $ 1,602 $ 1,602 $ — $ — Debt securities – municipal securities 2,524 — 2,524 — As of December 31, 2017 Money market funds 1,427 1,427 — — Debt securities – municipal securities 1,887 — 1,887 — (1) The money market funds and debt securities are trading securities and are restricted to meet statutory requirements. The carrying value, included within "Other long-term assets" in the Company's consolidated balance sheets, approximates the estimated fair value. Recurring Fair Value Measurements (Liabilities) — As of December 31, 2018 and 2017 , there were no major categories of liabilities included in the Company's consolidated balance sheets at estimated fair value that were measured on a recurring basis. Nonrecurring Fair Value Measurements (Assets) — The following table presents assets measured at estimated fair value on a nonrecurring basis as of December 31, 2018 and 2017 : Fair Value Measurements at Reporting Date Using Estimated Fair Value Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Losses (In thousands) As of December 31, 2018 Software (1) $ — $ — $ — $ — $ (550 ) Equipment (2) 2,800 — 2,800 — (2,248 ) As of December 31, 2017 Software (3) $ — $ — $ — $ — $ (16,746 ) Equipment (4) 350 — — 350 (98 ) (1) During the fourth quarter of 2018, the Company incurred impairment charges related to replaced software systems of $0.6 million . (2) During the fourth quarter of 2018, the Company incurred impairment charges related to the Company airplane of $2.2 million . This impairment was allocated between the Knight Trucking and Knight Logistics segments based on each segment’s use of the asset. (3) The Company terminated the implementation of Swift's ERP system in 2017. The related impairment loss was included in "Impairments" within operating income in the consolidated income statement (within Swift's non-reportable segments). (4) Management reassessed the fair value of certain Interstate Equipment Leasing, LLC tractors as of December 31, 2017 , which had a total book value of $0.4 million , determining that there was an impairment loss. The impairment loss was included in "Impairments" within operating income in the consolidated income statement (within Swift's non-reportable segments). Nonrecurring Fair Value Measurements (Liabilities) — As of December 31, 2018 and 2017 there were no liabilities included in the Company's consolidated balance sheets at estimated fair value that were measured on a nonrecurring basis.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
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: 2018 2017 2016 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) $ 681 $ — $ 161 $ — $ — $ — SME Industries (1) 698 — 275 — — — Total $ 1,379 $ — $ 436 $ — $ — $ — Facility and Equipment Leases: Central Freight Lines (1) $ 916 $ 370 $ 245 $ 92 $ — $ — Other Affiliates (1) 19 — — — — — Total $ 935 $ 370 $ 245 $ 92 $ — $ — Other Services: Updike Distribution Logistics, LLC (2) $ 554 $ — $ 2,771 $ — $ 1,433 $ — Other Affiliates (1) 35 2,590 48 604 — — Total $ 589 $ 2,590 $ 2,819 $ 604 $ 1,433 $ — (1) Entities affiliated with former Board member Jerry Moyes include Central Freight Lines, SME Industries, Compensi Services, and DPF Mobile. Transactions with these entities that are controlled by and/or are otherwise affiliated with Jerry Moyes, include freight services, facility leases, equipment sales, and other services. • Freight Services Provided by Knight-Swift — The Company charges for freight services to each of these companies for transportation services. • Freight Services Received by Knight-Swift — Transportation services received from Central Freight 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 and certain third-party payroll and employee benefits administration services from the identified related parties are included in other services received by the Company. • In conjunction with Swift's September 8, 2016 announcement that Jerry Moyes would retire from his position as Chief Executive Officer effective December 31, 2016, Swift entered into an agreement with Mr. Moyes to memorialize the terms of his retirement, which was assumed by Knight-Swift. Swift contracted with Mr. Moyes to serve as a non-employee consultant from January 1, 2017 through December 31, 2019 , during which time Swift will pay Mr. Moyes a monthly consulting fee in cash. The following is a rollforward of the accrued liability for the consulting fees: (In thousands) Accrued consulting fees – Jerry Moyes, balance at December 31, 2017 (1a) $ 4,450 Additions to accrual — Less: payments (2,225 ) Accrued consulting fees – Jerry Moyes, balance at December 31, 2018 (1a) $ 2,225 (1a) The balance is included in "Other long-term liabilities" (noncurrent) and "Accrued liabilities" (current) in the consolidated balance sheets, based on the timing of the expected payments. (2) Knight had an arrangement with Updike Distribution Logistics, LLC, a company that is owned by the father and three brothers of Executive Vice President of Sales and Marketing, James Updike, Jr. The arrangement allowed Updike Distribution Logistics, LLC to purchase fuel from Knight's vendors at cost, plus an administrative fee. The arrangement was terminated during the second quarter of 2018. Receivables and payables pertaining to related party transactions were: December 31, 2018 2017 Receivable Payable Receivable Payable (In thousands) Central Freight Lines $ 254 $ — $ 213 $ — SME Industries 24 — 79 — Other Affiliates — 20 — — Total $ 278 $ 20 $ 292 $ — Land Purchase — In November 2018, the Company purchased land in Perris, California for $7.7 million from former Board member Jerry Moyes. Share Repurchase — On December 27, 2018, the Company purchased 1,173,680 shares of the Company’s common stock from an entity controlled by Jerry Moyes, a former Board member of the Company. The shares were purchased for an aggregate purchase price of $29.3 million , or $24.98 per share. The per share purchase price represents a three cent per share discount from the closing price of the Company’s common stock on December 26, 2018. The Company purchased the shares under the Knight-Swift Repurchase Plan.

Information by Segment, Geograp

Information by Segment, Geography, and Customer Concentration	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Information by Segment, Geography, and Customer Concentration	Information by Segment, Geography, and Customer Concentration Segment Information The Company has six reportable segments, which are the historical reportable operating segments of Knight and Swift: Knight Trucking, Knight Logistics, Swift Truckload, Swift Dedicated, Swift Refrigerated, and Swift Intermodal, as well as the Swift non-reportable segments, discussed below. See Note 1 for information regarding the Company's anticipated segment realignment in the first quarter of 2019. See Note 2 for discussion of the Company's accounting policy related to segments. Trucking Segments: • Knight Trucking — The Knight Trucking segment is comprised of dry van, refrigerated, and drayage operations. Abilene's trucking operations are included beginning March 17, 2018. • Swift Truckload — The Swift Truckload segment consists of one-way movements over irregular routes throughout the US, Mexico, and Canada. • Swift Dedicated — The Swift Dedicated segment devotes use of equipment to specific customers and offers tailored solutions under long-term contracts. • Swift Refrigerated — The Swift Refrigerated segment primarily consists of shipments for customers that require temperature-controlled trailers. These shipments include one-way movements over irregular routes, as well as dedicated truck operations. Knight Logistics The Knight Logistics segment is primarily comprised of brokerage and intermodal operations. Knight also provides logistics freight management and other non-trucking services through its Knight Logistics business. Abilene's logistics operations are included beginning March 17, 2018. Swift Intermodal The Swift Intermodal segment includes revenue generated by moving freight over the rail in Swift's containers and other trailing equipment, combined with revenue for drayage to transport loads between the railheads and customer locations. Swift Non-reportable Segments The Swift non-reportable segments include Swift's logistics and freight brokerage services, as well as support services that Swift's subsidiaries provide to customers and independent contractors, including repair and maintenance shop services, equipment leasing and insurance. Certain of Swift's legal settlements and accruals, amortization of intangibles related to the 2017 Merger, and certain other corporate expenses are also included in the non-reportable segments. Intersegment Eliminations Certain operating segments provide transportation and related services for other affiliates outside their reportable segment. For Knight operating segments, such services are billed at cost, and no profit is earned. For Swift 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: 2018 2017 2016 Total revenue: (Dollars in thousands) Knight – Trucking $ 1,144,125 21.4 % $ 906,484 37.4 % $ 900,368 80.5 % Knight – Logistics $ 334,108 6.3 % $ 234,155 9.7 % $ 226,912 20.3 % Swift – Truckload $ 1,680,882 31.5 % $ 609,112 25.1 % $ — — % Swift – Dedicated $ 646,057 12.1 % $ 200,628 8.3 % $ — — % Swift – Refrigerated $ 819,190 15.3 % $ 254,102 10.5 % $ — — % Swift – Intermodal $ 470,165 8.8 % $ 130,441 5.4 % $ — — % Subtotal $ 5,094,527 95.4 % $ 2,334,922 96.4 % $ 1,127,280 100.8 % Non-reportable segments $ 314,732 5.8 % $ 115,530 4.8 % $ — — % Intersegment eliminations $ (65,193 ) (1.2 )% $ (24,999 ) (1.2 )% $ (9,246 ) (0.8 )% Total revenue $ 5,344,066 100.0 % $ 2,425,453 100.0 % $ 1,118,034 100.0 % 2018 2017 2016 Operating income (loss): (Dollars in thousands) Knight – Trucking $ 209,099 36.7 % $ 92,298 46.0 % $ 136,229 91.7 % Knight – Logistics $ 24,917 4.4 % $ 12,600 6.3 % $ 12,250 8.3 % Swift – Truckload $ 225,436 39.6 % $ 74,924 37.3 % $ — — % Swift – Dedicated $ 81,942 14.4 % $ 22,410 11.2 % $ — — % Swift – Refrigerated $ 34,341 6.0 % $ 13,626 6.8 % $ — — % Swift – Intermodal $ 30,127 5.3 % $ 5,977 3.0 % $ — — % Subtotal $ 605,862 106.4 % $ 221,835 110.6 % $ 148,479 100.0 % Non-reportable segments $ (36,819 ) (6.4 )% $ (21,205 ) (10.6 )% $ — — % Operating income $ 569,043 100.0 % $ 200,630 100.0 % $ 148,479 100.0 % 2018 2017 2016 Depreciation and amortization of property and equipment: (Dollars in thousands) Knight – Trucking $ 121,376 31.3 % $ 111,536 57.6 % $ 111,242 96.2 % Knight – Logistics $ 4,441 1.1 % $ 5,089 2.6 % $ 4,418 3.8 % Swift – Truckload $ 106,901 27.6 % $ 32,258 16.7 % $ — — % Swift – Dedicated $ 50,209 13.0 % $ 14,381 7.4 % $ — — % Swift – Refrigerated $ 40,724 10.5 % $ 11,163 5.8 % $ — — % Swift – Intermodal $ 11,951 3.1 % $ 3,231 1.7 % $ — — % Subtotal $ 335,602 86.6 % $ 177,658 91.8 % $ 115,660 100.0 % Non-reportable segments $ 51,903 13.4 % $ 16,075 8.2 % $ — — % Consolidated depreciation and amortization of property and equipment $ 387,505 100.0 % $ 193,733 100.0 % $ 115,660 100.0 % Geographical Information In aggregate, operating revenue from the Company's foreign operations was less than 5.0% of consolidated total revenue for each of 2018 , 2017 , and 2016 . Additionally, long-lived assets on the balance sheets of the Company's foreign subsidiaries were less than 5.0% of consolidated "Total assets" as of December 31, 2018 and 2017 . Customer Concentration Services provided to the Company's largest customer, Walmart, generated 14.6% and 12.5% of total revenue in 2018 and 2017 , respectively. Revenue generated by Walmart is reported in each of our reportable operating segments. No other customer accounted for 10.0% or more of total revenue in 2018 . No customer accounted for 10.0% or more of total revenue in 2016.

Quarterly Result Of Operations

Quarterly Result Of Operations (Unaudited)	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Information [Abstract]
Quarterly Results of Operations (Unaudited)	Quarterly Results of Operations (Unaudited) In management's opinion, the following summarized financial information fairly presents the Company's results of operations for the quarters noted. These results are not necessarily indicative of future quarterly results. First Quarter Second Quarter Third Quarter Fourth Quarter (In thousands, except per share data) 2018 Total revenue $ 1,271,132 $ 1,331,683 $ 1,346,611 $ 1,394,640 Net income 70,732 91,628 106,344 151,945 Net income attributable to Knight-Swift 70,364 91,323 105,881 151,696 Basic earnings per share 0.39 0.51 0.60 0.87 Diluted earnings per share 0.39 0.51 0.60 0.86 2017 Total revenue $ 271,182 $ 273,243 $ 521,608 $ 1,359,420 Net income 15,106 18,259 4,199 447,861 Net income attributable to Knight-Swift 14,876 17,970 3,881 447,564 Basic earnings per share 0.19 0.22 0.04 2.52 Diluted earnings per share 0.18 0.22 0.04 2.50

Introduction and Basis of Pre_2

Introduction and Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting, Policy [Policy Text Block]	In management's opinion, these consolidated financial statements were prepared in accordance with GAAP and include all adjustments necessary (consisting of normal recurring adjustments) for the fair presentation of the periods presented.
Consolidation, Policy [Policy Text Block]	With respect to transactional/durational data, references to "years", including "2018", "2017", "2016", "2015", and "2014" pertain to calendar years. Similarly, references to "quarters", including "first", "second", "third", and "fourth" pertain to calendar quarters. Note regarding comparability — Based on the structure of the 2017 Merger, the reported results do not include the results of operations of Swift and its subsidiaries on and prior to the 2017 Merger, in accordance with the accounting treatment applicable to the transaction. Additionally, the reported results do not include the results of operations of Abilene and its subsidiaries on and prior to its acquisition by the Company on March 16, 2018 in accordance with the accounting treatment applicable to the transaction. Accordingly, comparisons between the Company's 2018 results and prior periods may not be meaningful. Joint ventures — The financial activities of the following entities with which the Company has joint ventures are consolidated. The noncontrolling interest for these entities is presented as a separate component of the consolidated financial statements. • In 2014, Knight formed an Arizona limited liability company, now known as Kold Trans, LLC, for the purpose of expanding its refrigerated trucking business. Knight was entitled to 80.0% of the profits of the entity and has effective control over the management of the entity. During 2018, the Company purchased the remaining 20.0% of the joint venture, eliminating the related noncontrolling interest. • In 2010, Knight partnered with a non-related investor to form an Arizona limited liability company for the purpose of sourcing commercial vehicle parts. Knight acquired a 52.0% ownership interest in this entity. Equity and cost method investments — Refer to Note 8 for basis of presentation disclosures regarding Knight's equity and cost method investments in Transportation Resource Partners.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Use of Estimates, Policy [Policy Text Block]	Use of Estimates — The preparation of the consolidated financial statements, in accordance with GAAP, requires management to make estimates and assumptions about future events that affect the amounts reported in the Company's consolidated financial statements and accompanying notes. On an ongoing basis, management evaluates and periodically adjusts its estimates and assumptions, based on historical experience, the impact of the current economic environment, and other key factors. Volatile energy markets, as well as changes in consumer spending have increased the inherent uncertainty in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Significant items subject to such estimates and assumptions include: • carrying amount of property and equipment, intangibles, and goodwill; • valuation allowances for receivables, inventories, and deferred income tax assets; • valuation of financial instruments; • calculation of stock-based compensation; • estimates of claims accruals; • leases, and • contingent obligations.
Segments, Policy [Policy Text Block]	Segments — The Company uses the "management approach" to determine its reportable segments, as well as to determine the basis of reporting the operating segment information. Certain of the Company's operating segments have been aggregated into reportable segments. The management approach focuses on financial information that management uses to make operating decisions. The Company's chief operating decision makers use total revenue, operating expense categories, operating ratios, operating income, and key operating statistics to evaluate performance and allocate resources to the Company's operations. Operating income is the measure that management uses to evaluate segment performance and allocate resources. Operating income should not be viewed as a substitute for GAAP net income (loss). Management believes the presentation of operating income enhances the understanding of the Company's performance by highlighting the results of operations and the underlying profitability drivers of the business segments. Operating income is defined as "Total revenue" less "Operating expenses." Based on the unique nature of the Company's operating structure, certain revenue-generating assets are interchangeable between segments. Additionally, the Company's chief operating decision makers do not review assets or liabilities by segment to make operating decisions. The Company allocates depreciation and amortization expense of its property and equipment to the segments based on the actual utilization of the asset by the segment during the period. Revenue Disaggregation — In considering the level at which the Company should disaggregate revenues pertaining to contracts with customers, management determined that there are no significant differences between segments in how the nature, amount, timing, and uncertainty of revenue or cash flows are affected by economic factors. Additionally, management considered how and where the Company has communicated information about revenue for various purposes, including disclosures outside of the financial statements and how information is regularly reviewed by the Company's chief operating decision makers for evaluating financial performance of the Company's segments, among others. Based on these considerations, management determined that revenues should be disaggregated by reportable segment.
Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents — Cash and cash equivalents are comprised of cash, money market funds, and highly liquid instruments with insignificant interest rate risk and original maturities of three months or less. Cash balances with institutions may be in excess of Federal Deposit Insurance Corporation ("FDIC") limits or may be invested in sweep accounts that are not insured by the institution, the FDIC, or any other government agency. Restricted Cash — The Company's wholly-owned captive insurance companies, Red Rock and Mohave, maintain certain operating bank accounts, working trust accounts, and investment accounts. The cash and short-term investments within the accounts are restricted by insurance regulations to fund the insurance claim losses to be paid by the captive insurance companies. Therefore, these cash and short-term investments are classified as "Cash and cash equivalents – restricted" in the consolidated balance sheets.
Restricted Investments, Policy [Policy Text Block]	Restricted Investments — The Company's investments are restricted by insurance regulations to fund the insurance claim losses to be paid by the captive insurance companies. The Company accounts for its investments in accordance with ASC 320, Investments – Debt Securities . Management determines the appropriate classification of its investments in debt securities at the time of purchase and re-evaluates the determination on a quarterly basis. As of December 31, 2018 , all of the Company's investments in fixed-maturity securities were classified as held-to-maturity, as the Company has the positive intent and ability to hold these securities to maturity. Held-to-maturity securities are carried at amortized cost. The amortized cost of debt securities is adjusted using the effective interest rate method for amortization of premiums and accretion of discounts. Amortization and accretion are reported in "Other income, net" in the consolidated income statements. Management periodically evaluates restricted investments for impairment. The assessment of whether impairments have occurred is based on management's case-by-case evaluation of the underlying reasons for the decline in estimated fair value. Management accounts for other-than-temporary impairments of debt securities in accordance with ASC 320, Investments – Debt Securities . This guidance requires the Company to evaluate whether it intends to sell an impaired debt security or whether it is more likely than not that it will be required to sell an impaired debt security before recovery of the amortized cost basis. If either of these criteria are met, an impairment loss equal to the difference between the debt security's amortized cost and its estimated fair value is recognized in earnings. For impaired debt securities that do not meet these criteria, the Company determines if a credit loss exists with respect to the impaired security. If a credit loss exists, the credit loss component of the impairment (i.e., the difference between the security's amortized cost and the present value of projected future cash flows expected to be collected) is recognized in earnings and the remaining portion of the impairment is recognized as a component of accumulated other comprehensive income.
Inventories and Supplies, Policy [Policy Text Block]	Inventories and Supplies — Inventories and supplies, which are included in "Other current assets" in the consolidated balance sheets, primarily consist of spare parts, tires, fuel, and supplies and are stated at lower of cost or net realizable value. Depending on the class of inventory, cost is determined using the first-in, first-out method or average cost.
Property and Equipment, Policy [Policy Text Block]	Property and Equipment — Property and equipment is stated at cost less accumulated depreciation. Costs to construct significant assets include capitalized interest incurred during the construction and development period. Expenditures for replacements and improvements are capitalized. Maintenance and repairs are expensed as incurred. Depreciation of property and equipment is calculated on a straight-line basis down to the salvage value, as applicable, over the following estimated useful lives: Category: Range (in years) Revenue equipment 4 — 20 Shop and service equipment 2 — 10 Land improvements 5 — 15 Buildings and building improvements 10 — 40 Furniture and fixtures 3 — 10 Leasehold improvements Life of the lease Net gains on the disposal of property and equipment are presented in the consolidated income statements within "Miscellaneous operating expenses." Tires on purchased revenue equipment are capitalized along with the related equipment cost when the vehicle is placed in service, and are depreciated over the life of the vehicle. Replacement tires are classified as inventory and expensed when placed in service. Management evaluates its property and equipment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable in accordance with ASC 360, Property, Plant and Equipment . When such events or changes in circumstances occur, management performs a recoverability test that compares the carrying amount with the projected undiscounted cash flows from the use and eventual disposition of the asset or asset group. An impairment is recorded for any excess of the carrying amount over the estimated fair value. Fair value is determined through various valuation techniques including discounted cash flow models, quoted market values, and third-party independent appraisals, as considered necessary.
Intangible Assets other than Goodwill, Policy [Policy Text Block]	Intangible Assets other than Goodwill — The Company's intangible assets other than goodwill primarily consist of acquired customer relationships and trade names from the 2017 Merger, as well as intangibles from Knight's 2018 acquisition of Abilene, and Knight's 2014 acquisition of Barr-Nunn Transportation, Inc. and certain of its affiliates. Amortization of acquired customer relationships is calculated on a straight-line basis over the estimated useful life, which ranges from 5 years to 20 years . The trade names have indefinite useful lives and are not amortized, but are tested for impairment at least annually, unless events occur or circumstances change between annual tests that would more likely than not reduce the fair value. Management reviews its intangible assets for impairment whenever events or circumstances indicate that the carrying amount of the asset may not be recoverable, in accordance with ASC 350, Intangibles – Goodwill and Other. When such events or changes in circumstances occur, management performs a recoverability test that compares the carrying amount with the projected discounted cash flows from the use and eventual disposition of the asset or asset group. An impairment is recorded for any excess of the carrying amount over the estimated fair value, which is generally determined using discounted future cash flows.
Goodwill, Policy [Policy Text Block]	Goodwill — Management evaluates goodwill on an annual basis as of June 30 th , or more frequently if indicators of impairment exist. The Company assesses qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than the carrying amount. If the Company concludes that it is more likely than not that the fair value of a reporting unit is less than its carrying amount, the Company conducts a two -step quantitative goodwill impairment test. The first step of the quantitative impairment test involves comparing the fair values of the applicable reporting units with their carrying values. Management estimates the fair values of its reporting units using a combination of the income and market approaches. If the carrying amount of a reporting unit exceeds the reporting unit's fair value, then management performs the second step of the quantitative impairment test. The second step of the quantitative impairment test involves comparing the implied fair value of the affected reporting unit's goodwill with the carrying value of that goodwill. Any amount by which the carrying value of the goodwill exceeds its implied fair value is recognized as an impairment loss. Refer to Note 12 for discussion of the results of the Company's annual evaluation as of June 30, 2018 .
Claims Accruals, Policy [Policy Text Block]	Claims Accruals — The Company is self-insured for a portion of its risk related to auto liability, workers' compensation, property damage, and cargo damage. Self-insurance results from buying insurance coverage that applies in excess of a retained portion of risk for each respective line of coverage. The Company accrues for the cost of the uninsured portion of pending claims by evaluating the nature and severity of individual claims and by estimating future claims development based upon historical claims development trends. The actual cost to settle self-insured claim liabilities may differ from the Company's reserve estimates due to legal costs, claims that have been incurred but not reported, and various other uncertainties, including the inherent difficulty in estimating the severity of the claims and the potential judgment or settlement amount to dispose of the claim.
Operating Leases, Policy [Policy Text Block]	In accordance with ASC 840, Leases , property and equipment held under operating leases, and liabilities related thereto, are off-balance sheet. All expenses related to operating leases are reflected in the consolidated income statements in "Rental expense." At lease inception, management determines whether the lease should be classified as operating or capital lease, based on the guidance set forth in ASC 840. Additionally at lease inception, management determines the useful life and estimates residual values of the related equipment. Future minimum lease payments used in determining lease classification represent the minimum rental payments called for over the lease term, inclusive of residual value guarantees (if applicable) and amounts that would be required to be paid, if any, by the Company upon default for leases containing subjective acceleration or cross default clauses. In connection with various operating leases, we issued residual value guarantees, which provide that if we do not purchase the leased equipment from the lessor at the end of the lease term, we are liable to the lessor for an amount equal to the shortage (if any) between the proceeds from the sale of the equipment and an agreed value. To the extent we believe any manufacturer will refuse or be unable to meet its obligation, we recognize additional rental expense to the extent we believe the fair market value at the lease termination will be less than our obligation to the lessor. We believe that proceeds from the sale of equipment under operating leases would exceed the payment obligation on substantially all operating leases.
Fair Value Measurement, Policy [Policy Text Block]	The estimated fair values of the financial instruments shown in the above table as of December 31, 2018 and 2017 , 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 the Company'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 is based on quoted prices in active markets that are readily and regularly obtainable. See Note 7 for additional investments disclosures regarding restricted investments, held-to-maturity. Term Loan — The estimated fair value of the Term Loan approximates the face value. See Note 17 for additional debt disclosures. Accounts Receivable Securitization — The Company's securitization of accounts receivable consists of borrowings outstanding pursuant to the 2018 RSA as of December 31, 2018 and the 2015 RSA as of December 31, 2017 , as discussed in Note 16 . The estimated fair value of the 2018 RSA and 2015 RSA approximates the face value. Fair Value Hierarchy — ASC 820 establishes a framework for measuring fair value in accordance with GAAP and expands financial statement disclosure requirements for fair value measurements. ASC 820 further specifies a hierarchy of valuation techniques, which is based on whether the inputs into the valuation technique are observable or unobservable. The hierarchy follows: • Level 1 — Valuation techniques in which all significant inputs are quoted prices from active markets for assets or liabilities that are identical to the assets or liabilities being measured. • Level 2 — Valuation techniques in which significant inputs include quoted prices from active markets for assets or liabilities that are similar to the assets or liabilities being measured and/or quoted prices from markets that are not active for assets or liabilities that are identical or similar to the assets or liabilities being measured. Also, model-derived valuations in which all significant inputs and significant value drivers are observable in active markets are Level 2 valuation techniques. • Level 3 — Valuation techniques in which one or more significant inputs or significant value drivers are unobservable. Unobservable inputs are valuation technique inputs that reflect the Company's own assumptions about the assumptions that market participants would use in pricing an asset or liability. When available, the Company uses quoted market prices to determine the estimated fair value of an asset or liability. If quoted market prices are not available, the Company measures fair value using valuation techniques that use, when possible, current market-based or independently-sourced market parameters, such as interest rates and currency rates. The level in the fair value hierarchy within which a fair value measurement in its entirety falls is based on the lowest level input that is significant to the estimated fair value measurement in its entirety.
Contingencies, Policy [Policy Text Block]	The Company is involved in certain claims and pending litigation primarily arising in the normal course of business. The majority of these claims relate to workers' compensation, auto collision and liability, physical damage, and cargo damage, as well as certain class action litigation in which plaintiffs allege failure to provide meal and rest breaks, unpaid wages, unauthorized deductions, and other items. The Company accrues for the uninsured portion of claims losses and the gross amount of other losses when the likelihood of the loss is probable and the amount of the loss is reasonably estimable. These accruals are based on management's best estimate within a possible range of loss. When there is no amount within the range of loss that appears to be a better estimate than any other amount, then management accrues to the low end of the range. Legal fees are expensed as incurred. When it is reasonably possible that exposure exists in excess of the related accrual (which could be no accrual), management discloses an estimate of the possible loss or range of loss, unless an estimate cannot be determined (because, among other reasons, (1) the proceedings are in various stages that do not allow for assessment; (2) damages have not been sought; (3) damages are unsupported and/or exaggerated; (4) there is uncertainty as to the outcome of pending appeals; and/or (5) there are significant factual issues to be resolved). If the likelihood of a loss is remote, the Company does not accrue for the loss. However, if the likelihood of a loss is remote, but it is at least reasonably possible that one or more future confirming events may materially change management's estimate within twelve months from the date of the financial statements, management discloses an estimate of the possible loss or range of loss, unless an estimate cannot be determined.
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition (2018) — The Company adopted ASC 606, Revenue from Contracts with Customers , on January 1, 2018. See Note 3 for the impact of this standard on the Company's revenue recognition accounting policies. • Contract Identification — Management has identified that a legally enforceable contract with its customers is executed by both parties at the point of pickup at the shipper's location, as evidenced by the bill of lading. Although the Company may have master agreements with its customers, these master agreements only establish general terms. There is no financial obligation to the shipper until the load is tendered/accepted and the Company takes possession of the load. • Performance Obligations — The Company's only performance obligation is transportation services. The Company's delivery, accessorial, and dedicated operations truck capacity in its dedicated operations represent a bundle of services that are highly interdependent and have the same pattern of transfer to the customer. These services are not capable of being distinct from one another. For example, the Company generally would not provide accessorial services or truck capacity without providing delivery services. • Transaction Price — Depending on the contract, the total transaction price may consist of mileage revenue, fuel surcharge revenue, accessorial fees, truck capacity, and/or non-cash consideration. Non-cash consideration is measured by the estimated fair value of the non-cash consideration at contract inception. There is no significant financing component in the transaction price, as the Company's customers generally pay within the contractual payment terms of 30 to 60 days. • Allocating Transaction Price to Performance Obligations — The transaction price is entirely allocated to the only performance obligation: transportation services. • Revenue Recognition — The performance obligation of providing transportation services is satisfied over time. Accordingly, revenue is recognized over time. Management estimates the amount of revenue in transit at period end based on the number of days completed of the dispatch (which is generally one to three days for the trucking segments, but can be longer for intermodal operations). Management believes this to be a faithful depiction of the transfer of services because if a load is dispatched, but terminates mid-route and the load is picked up by another carrier, then that carrier would not need to re-perform the services for the days already traveled. Recognizing revenue over time is a change from the Company's past practice, under which revenue was recognized at the point in time that the freight was delivered. Due to this change, the timing of revenue recognition (as well as the related variable costs) between reportable periods will change, compared to revenue recognition under ASC 605, Revenue Recognition . However, the net impact on the Company's results of operations on the current reportable period is immaterial and is expected to continue to be immaterial in future reportable periods. There was no change in management's determination that the Company acts as the principal (rather than the agent) with respect to revenue recognition within its logistics businesses, under ASC 606, compared to ASC 605. Accordingly, the Company continues to recognize revenue on a gross basis, consistent with past practices. Significant judgments involved in the Company's revenue recognition and corresponding accounts receivable balances include: • Measuring in-transit revenue at period end (discussed above). • Estimating the allowance for doubtful accounts. The Company establishes an allowance for doubtful accounts based on historical experience and any known trends or uncertainties related to customer billing and account collectability. Management reviews the adequacy of its allowance for doubtful accounts on a quarterly basis. Uncollectible accounts are written off when deemed uncollectible, and accounts receivable are presented net of an allowance for doubtful accounts. The Company recognizes operating lease revenue from leasing tractors and related equipment to independent contractors. Operating lease revenue from rental operations is recognized as earned, which is straight-lined per the rent schedules in the lease agreements. Losses from lease defaults are recognized as offsets to revenue. Revenue Recognition (2016 and 2017) — In accordance with ASC 605-20-25-13, Services for Freight-in-Transit at the End of a Reporting Period, the Company recognized operating revenue and the related direct costs of such revenue when persuasive evidence of an arrangement existed, the fee was fixed and determinable, and collectability was probable, all of which occurred as of the date the freight was delivered. Credit terms for customer accounts are generally on a net 30 day basis. The Company establishes an allowance for doubtful accounts based on historical experience and any known trends or uncertainties related to customer billing and account collectability. The Company reviews the adequacy of its allowance for doubtful accounts on a quarterly basis. Uncollectible accounts are written off when deemed uncollectible, and accounts receivable are presented net of an allowance for doubtful accounts.
Stock-based Compensation, Policy [Policy Text Block]	Stock-based Compensation — The Company accounts for stock-based compensation expense in accordance with ASC 718, Compensation – Stock Compensation. ASC 718 requires that all share-based payments to employees and non-employee directors, including grants of employee stock options, be recognized in the financial statements based upon a grant-date fair value of an award. The fair value of performance units is estimated using the Monte Carlo Simulation valuation model. Equity awards settled in cash are remeasured at each reporting period and are recognized as a liability in the consolidated balance sheets during the vesting period until settlement. The fair value of stock options is estimated using the Black-Scholes option-valuation model. The Company calculates the number of awards expected to vest as awards granted, less expected forfeitures over the life of the award (estimated at grant date). Compensation expense is recorded on a straight-line basis, by amortizing the grant-date fair value over the requisite service period of the entire award. Unless a material deviation from the assumed forfeiture rate is observed during the term in which the awards are expensed, any adjustment necessary to reflect differences in actual experience is recognized in the period the award becomes payable or exercisable.
Income Taxes, Policy [Policy Text Block]	Income Taxes — Management accounts for income taxes under the asset and liability method. Accordingly, deferred tax assets and liabilities are recognized for the future tax consequences of events that have been included in the consolidated financial statements. Additionally, deferred tax assets and liabilities are determined based on the differences between the financial statement carrying amounts and respective tax bases of assets and liabilities (using enacted tax rates in effect for the year in which the differences are expected to reverse). The effect on deferred tax assets and liabilities of changes in tax rates is recognized in income in the period that includes the enactment date. Net deferred incomes taxes are classified as noncurrent in the consolidated balance sheets. A valuation allowance is provided against deferred tax assets if the Company determines it is more likely than not that such assets will not ultimately be realized. In making such determinations, the Company considers all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax planning strategies, and recent financial operations. Unrecognized tax benefits are defined as the difference between a tax position taken or expected to be taken in a tax return and the benefit recognized and measured pursuant to ASC 740, Income Taxes . The Company does not recognize a tax benefit for uncertain tax positions unless it concludes that it is more likely than not that the benefit will be sustained on audit (including resolutions of any related appeals or litigation processes) by the taxing authority, based solely on the technical merits of the associated tax position. If the recognition threshold is met, the Company recognizes a tax benefit measured at the largest amount of the tax benefit that, in the management's judgment, is greater than 50% likely to be realized. The Company records expected incurred interest and penalties related to unrecognized tax positions in "Income tax (benefit) expense" in the consolidated income statements. To the extent interest and penalties are not assessed with respect to uncertain tax positions, amounts accrued will be reduced and reflected as a reduction of the overall income tax provision.

Recently Adopted Accounting P_2

Recently Adopted Accounting Pronouncements (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Changes and Error Corrections [Abstract]
Equity Method Investments [Policy Text Block]	As allowed by the amendments in ASU 2016-15, the Company elected to apply the "Nature of Distribution" approach to classifying cash flows from its equity method investments in Transportation Resource Partners. However, retrospectively applying this approach did not change the presentation of the first quarter 2017 statement of cash flows.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Property, Plant and Equipment [Table Text Block]	Depreciation of property and equipment is calculated on a straight-line basis down to the salvage value, as applicable, over the following estimated useful lives: Category: Range (in years) Revenue equipment 4 — 20 Shop and service equipment 2 — 10 Land improvements 5 — 15 Buildings and building improvements 10 — 40 Furniture and fixtures 3 — 10 Leasehold improvements Life of the lease

Recently Adopted Accounting P_3

Recently Adopted Accounting Pronouncements (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Changes and Error Corrections [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]	The cumulative effect of changes made to the Company's consolidated opening balance sheet for the adoption of ASC 606 is presented below. December 31, Opening Balance Adjustments January 1, (in thousands) Assets Trade receivables, net of allowance for doubtful accounts $ 574,265 $ 16,992 $ 591,257 Liabilities Accrued payroll and purchased transportation $ 107,017 $ 9,720 $ 116,737 Accrued liabilities 186,076 201 186,277 Deferred tax liabilities 679,077 1,770 680,847 Equity Retained earnings $ 1,016,738 $ 5,301 $ 1,022,039 Current Period Impact of Adoption — The required quantitative disclosures regarding the current period impact of adopting ASC 606 on the consolidated income statement and balance sheet are presented below. The effect of change amounts are entirely attributed to the in-transit accrual from the Company recognizing revenue over time under ASC 606, compared to recognizing revenue at a point in time under ASC 605. 2018 Income Statement As Reported Under ASC 606 If Reported Under ASC 605 Effect of Change to ASC 606 (in thousands) Revenue Revenue, excluding fuel surcharge $ 4,725,288 $ 4,726,578 $ (1,290 ) Fuel surcharge revenue 618,778 618,878 (100 ) Impact on total revenue (1,390 ) Operating Expenses Salaries, wages, and benefits $ 1,495,126 $ 1,495,480 $ 354 Operations and maintenance 340,627 340,645 18 Purchased transportation 1,318,303 1,318,546 243 Impact on total operating expenses 615 Other Expenses Income tax expense $ 131,389 $ 131,613 $ 224 Impact on net income attributable to Knight-Swift $ (551 ) December 31, 2018 Balance Sheet As Reported Under ASC 606 If Reported Under ASC 605 Effect of Change to ASC 606 (in thousands) Assets Trade receivables, net of allowance for doubtful accounts $ 616,830 $ 601,228 $ 15,602 Liabilities Accrued payroll and purchased transportation $ 126,464 $ 117,341 $ 9,123 Accrued liabilities 151,500 152,506 (1,006 ) Deferred tax liabilities 739,538 736,803 2,735 Equity Retained earnings $ 1,216,852 $ 1,212,102 $ 4,750 The table below summarizes the impact on the statement of cash flows of adopting ASU 2016-18, including changes made to the statement of cash flows captions. As allowed by the amendments in ASU 2016-15, the Company elected to apply the "Nature of Distribution" approach to classifying cash flows from its equity method investments in Transportation Resource Partners. However, retrospectively applying this approach did not change the presentation of the first quarter 2017 statement of cash flows. There were no other cash flow issues in ASU 2016-15 that impacted the Company's statement of cash flows presentation. 2017 As Reported ASU 2016-15 Reclassifications ASU 2016-18 Reclassifications Adjusted (in thousands) Other adjustments to reconcile net income to net cash provided by operating activities (1) $ 10,737 $ 4,021 $ — $ 14,758 Net cash provided by operating activities 318,569 4,021 — 322,590 (Increase) decrease in cash and cash equivalents - restricted (10,215 ) — 10,215 — Net cash, restricted cash, and equivalents acquired from mergers and acquisitions (2) 28,493 — 63,467 91,960 Other cash flows from investing activities (1) 13,957 (4,021 ) 17 9,953 Net cash used in investing activities (273,941 ) (4,021 ) 73,699 (204,263 ) Net increase in cash, restricted cash, and equivalents $ 68,628 $ — $ 73,699 $ 142,327 Cash, restricted cash, and equivalents at beginning of period 8,021 — 1,385 9,406 Cash, restricted cash, and equivalents at end of period $ 76,649 $ — $ 75,084 $ 151,733 (1) See Note 1 for line items that were previously separately presented, but are included in "Other adjustments to reconcile net income to net cash provided by operating activities" and "Other cash flows from investing activities" for the current period presentation. (2) The caption, as previously filed, was "Cash and cash equivalents received with 2017 Merger." 2016 As Reported ASU 2016-15 Reclassifications ASU 2016-18 Reclassifications Adjusted (in thousands) Other adjustments to reconcile net income to net cash provided by operating activities (1) $ 380 $ 422 $ — $ 802 Net cash provided by operating activities 243,354 422 — 243,776 (Increase) decrease in cash and cash equivalents - restricted (6 ) — 6 — Other cash flows from investing activities (1) (12,013 ) (422 ) 376 (12,059 ) Net cash (used in) provided by investing activities (101,020 ) (422 ) 382 (101,060 ) Net (increase) decrease in cash, restricted cash, and equivalents $ (670 ) $ — $ 382 $ (288 ) Cash, restricted cash, and equivalents at beginning of period 8,691 — 1,003 9,694 Cash, restricted cash, and equivalents at end of period $ 8,021 $ — $ 1,385 $ 9,406 (1) See footnote (1) in table above. Reconciliation of Cash, Restricted Cash, and Equivalents — The following table reconciles cash, restricted cash, and equivalents per the consolidated statements of cash flows to the consolidated balance sheets. December 31, December 31, December 31, (in thousands) Balance Sheets Cash and cash equivalents $ 82,486 $ 76,649 $ 8,021 Cash and cash equivalents – restricted 46,888 73,657 — Other long-term assets 1,602 1,427 1,385 Statement of Cash Flows Cash, restricted cash, and equivalents $ 130,976 $ 151,733 $ 9,406 Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact December 2018 2018-20: Leases – (Topic 842) Narrow-Scope Improvements for Lessors The amendments in this ASU provide entities with additional guidance about the recognition of variable payments for contracts with lease and nonlease components. These amendments provide lessors the option to exclude certain lessor costs from recognition. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below November 2018 2018-19: Codification Improvements to Topic 326 – Financial Instruments – Credit Losses The amendments in this ASU make targeted improvements to the implementation guidance in ASU 2016-13. The amendments clarify that receivables arising from operating leases are not within the scope of ASC 326-20, but instead should be accounted for in accordance with Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2020, Modified retrospective Currently under evaluation, but not expected to be material August 2018 2018-15: Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract The amendments align the requirements for capitalizing implementation costs in a hosting arrangement with the guidance for internal-use software, resulting in expensing preliminary or post-implementation project costs and capitalizing certain application development costs. The capitalized costs should be included in the balance sheet line that includes prepayment for the fees of the associated hosting arrangement, and amortized over the noncancellable period of the arrangement. Amortization expense should be included in the income statement line that includes the fees associated with the hosting element of the arrangement. Payments for capitalized implementation costs should be classified in the statement of cash flows in the same manner as payments made for hosting element fees. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2020, Prospective Currently under evaluation, but not expected to be material August 2018 2018-13: Fair Value Measurement (Topic 820): Disclosure Framework – Change to the Disclosure Requirements for Fair Value Measurement The amendments in this ASU modify several disclosure requirements under Topic 820. These changes include removing the disclosure requirements related to the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, and adding disclosure requirements about the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Additionally, the amendments remove the phrase "at a minimum" from the codification clarifying that materiality should be considered when evaluating disclosure requirements. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2019, Retrospective Not expected to be material (1) Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact July 2018 2018-11: Leases (Topic 842): Targeted Improvements The amendments in this ASU provide entities with an additional transition method for implementing ASC Topic 842, in which entities have the option to apply the new standard at the adoption date, recognizing a cumulative-effect adjustment to the opening balance of retained earnings. Comparative periods would not be restated, and would instead be presented under the legacy ASC Topic 840 guidance. Under certain conditions, the amendments in this ASU also provide lessors a practical expedient regarding separating nonlease components from the associated lease components if the nonlease components would otherwise be accounted for under ASC Topic 606, Revenue from Contracts with Customers. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below July 2018 2018-10: Leases (Topic 842): Codification Improvements This ASU contains various amendments to ASC Topic 842 that clarify the language, remove inconsistencies, and improve upon other issues, including those associated with implementing the new standard. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below June 2018 2018-07: Compensation – Improvements to Nonemployee Share-Based Payment Accounting The amendments in this ASU expand the scope of ASC Topic 718 to include share-based payments to nonemployees, and for public business entities include 1) measuring awards to nonemployees at grant-date fair value, 2) measuring awards to nonemployees at the grant date, 3) for awards with performance conditions granted to nonemployees, assessing the probability of satisfying performance conditions when measuring such awards, and 4) generally subjecting equity-classified awards to the requirements of ASC Topic 718, eliminating the requirement to reassess classification upon vesting. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. January 2019, Modified retrospective Currently under evaluation (2) January 2018 2018-01: Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842 The amendments in this ASU permit entities to elect to exclude land easements which were not previously recorded as leases from the evaluation related to the adoption of ASC Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below January 2017 2017-04: Intangibles – Goodwill and Other (Topic 350) Simplifying the Test for Goodwill Impairment The amendments in this ASU are intended to simplify subsequent measurement of goodwill. The key amendment in the ASU eliminates Step 2 from the goodwill impairment test, in which entities measured a goodwill impairment loss by comparing the implied fair value to the carrying amount of a reporting unit's goodwill. Instead, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value with the carrying amount of a reporting unit and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value. January 2020, prospective Currently under evaluation; not expected to be material Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact June 2016 2016-13: Financial Instruments – Credit Losses (Topic 326) – Measurement of Credit Losses on Financial Instruments The purpose of this ASU is to amend the current incurred loss impairment methodology with a new methodology that reflects expected credit losses and requires a broader range of reasonable and supportable information to inform credit loss estimates. This is the final credit accounting standard, out of a series, with detailed guidance on the new loss reserve model, Current Expected Credit Loss ("CECL"). Among other provisions, the amendments in the ASU require a financial asset (or group of assets) measured at amortized cost basis to be presented at the net amount expected to be collected. Entities are no longer required to wait until a loss is probable to record it. January 2020, Adoption method varies by amendment Currently under evaluation; not expected to be material February 2016 2016-02: Leases (Topic 842) The new standard requires lessees to recognize assets and liabilities arising from both operating and financing leases on the balance sheet. Lessor accounting for leases is largely unaffected. For public business entities, the new standard is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. January 2019, Modified retrospective - cumulative-effect adjustment to beginning balance of retained earnings at the adoption date Expected to be material (3) (1) ASU 2018-13: Fair Value Measurement (Topic 820): Disclosure Framework – Change to the Disclosure Requirements for Fair Value Measurement — Upon adoption, management expects to have fewer disclosures regarding its fair value measurements as a result of the amendments that eliminate "at a minimum" from the phrase, "an entity shall disclose at a minimum." The amendments are intended to allow entities to exercise discretion when considering fair value disclosures, including materiality considerations. Accordingly, the Company will exclude immaterial disclosures regarding fair value measurements from its quarterly and annual reports upon adoption, beginning in the first quarter of 2019. (2) ASU 2018-07: Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting — In accordance with the amendments in this ASU, the Company will be required to measure any nonemployee liability-classified awards that have not been settled by the adoption date and any equity-classified awards for which a measurement date has not been established through a cumulative-effect adjustment to retained earnings as of January 1, 2019. The Company is not expecting a material impact from adopting the amendments in this ASU, as the Company will have no unvested share-based payment awards related to its nonemployee directors as of January 1, 2019. (3) ASC 842, Leases — The Company established an implementation team, which includes support from external experts, to transition the Company from accounting for leases under ASC 840 to accounting for leases under ASC 842. The diagnostic phase of implementing the new standard is complete, and management has selected practical expedients and accounting policies to evaluate the lease population. The Company is substantially complete with the process of extracting and uploading lease data available from existing systems and documents into its new lease software solution. Management expects to elect the package of practical expedients (regarding lease identification, lease classification, and initial direct costs), but not the hindsight practical expedient. Additionally, management expects to elect accounting policies to account for its revenue equipment leases at the portfolio level, to bundle nonlease components with their related lease components (as lessee), and to not recognize a right-of-use asset or lease liability for short-term leases. These policies are not substantially different from the Company’s current accounting policies. After considering the above practical expedient and accounting policy elections, management expects that adopting the new lease standard will result in adding right-of-use assets of $270.0 million to $300.0 million and corresponding lease liabilities of $270.0 million to $300.0 million to the consolidated balance sheet as of January 1, 2019, with the net impact being recorded as a cumulative-effect adjustment to retained earnings, as applicable. The impact of adopting the new lease standard is not expected to be material to the Company’s consolidated income statement, liquidity, or compliance with debt covenants. Since management is continuing to evaluate the impacts of the above standards, disclosures around these preliminary assessments are subject to change.

Recently Issued Accounting Pr_2

Recently Issued Accounting Pronouncements (Tables)	12 Months Ended
	Dec. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]	The cumulative effect of changes made to the Company's consolidated opening balance sheet for the adoption of ASC 606 is presented below. December 31, Opening Balance Adjustments January 1, (in thousands) Assets Trade receivables, net of allowance for doubtful accounts $ 574,265 $ 16,992 $ 591,257 Liabilities Accrued payroll and purchased transportation $ 107,017 $ 9,720 $ 116,737 Accrued liabilities 186,076 201 186,277 Deferred tax liabilities 679,077 1,770 680,847 Equity Retained earnings $ 1,016,738 $ 5,301 $ 1,022,039 Current Period Impact of Adoption — The required quantitative disclosures regarding the current period impact of adopting ASC 606 on the consolidated income statement and balance sheet are presented below. The effect of change amounts are entirely attributed to the in-transit accrual from the Company recognizing revenue over time under ASC 606, compared to recognizing revenue at a point in time under ASC 605. 2018 Income Statement As Reported Under ASC 606 If Reported Under ASC 605 Effect of Change to ASC 606 (in thousands) Revenue Revenue, excluding fuel surcharge $ 4,725,288 $ 4,726,578 $ (1,290 ) Fuel surcharge revenue 618,778 618,878 (100 ) Impact on total revenue (1,390 ) Operating Expenses Salaries, wages, and benefits $ 1,495,126 $ 1,495,480 $ 354 Operations and maintenance 340,627 340,645 18 Purchased transportation 1,318,303 1,318,546 243 Impact on total operating expenses 615 Other Expenses Income tax expense $ 131,389 $ 131,613 $ 224 Impact on net income attributable to Knight-Swift $ (551 ) December 31, 2018 Balance Sheet As Reported Under ASC 606 If Reported Under ASC 605 Effect of Change to ASC 606 (in thousands) Assets Trade receivables, net of allowance for doubtful accounts $ 616,830 $ 601,228 $ 15,602 Liabilities Accrued payroll and purchased transportation $ 126,464 $ 117,341 $ 9,123 Accrued liabilities 151,500 152,506 (1,006 ) Deferred tax liabilities 739,538 736,803 2,735 Equity Retained earnings $ 1,216,852 $ 1,212,102 $ 4,750 The table below summarizes the impact on the statement of cash flows of adopting ASU 2016-18, including changes made to the statement of cash flows captions. As allowed by the amendments in ASU 2016-15, the Company elected to apply the "Nature of Distribution" approach to classifying cash flows from its equity method investments in Transportation Resource Partners. However, retrospectively applying this approach did not change the presentation of the first quarter 2017 statement of cash flows. There were no other cash flow issues in ASU 2016-15 that impacted the Company's statement of cash flows presentation. 2017 As Reported ASU 2016-15 Reclassifications ASU 2016-18 Reclassifications Adjusted (in thousands) Other adjustments to reconcile net income to net cash provided by operating activities (1) $ 10,737 $ 4,021 $ — $ 14,758 Net cash provided by operating activities 318,569 4,021 — 322,590 (Increase) decrease in cash and cash equivalents - restricted (10,215 ) — 10,215 — Net cash, restricted cash, and equivalents acquired from mergers and acquisitions (2) 28,493 — 63,467 91,960 Other cash flows from investing activities (1) 13,957 (4,021 ) 17 9,953 Net cash used in investing activities (273,941 ) (4,021 ) 73,699 (204,263 ) Net increase in cash, restricted cash, and equivalents $ 68,628 $ — $ 73,699 $ 142,327 Cash, restricted cash, and equivalents at beginning of period 8,021 — 1,385 9,406 Cash, restricted cash, and equivalents at end of period $ 76,649 $ — $ 75,084 $ 151,733 (1) See Note 1 for line items that were previously separately presented, but are included in "Other adjustments to reconcile net income to net cash provided by operating activities" and "Other cash flows from investing activities" for the current period presentation. (2) The caption, as previously filed, was "Cash and cash equivalents received with 2017 Merger." 2016 As Reported ASU 2016-15 Reclassifications ASU 2016-18 Reclassifications Adjusted (in thousands) Other adjustments to reconcile net income to net cash provided by operating activities (1) $ 380 $ 422 $ — $ 802 Net cash provided by operating activities 243,354 422 — 243,776 (Increase) decrease in cash and cash equivalents - restricted (6 ) — 6 — Other cash flows from investing activities (1) (12,013 ) (422 ) 376 (12,059 ) Net cash (used in) provided by investing activities (101,020 ) (422 ) 382 (101,060 ) Net (increase) decrease in cash, restricted cash, and equivalents $ (670 ) $ — $ 382 $ (288 ) Cash, restricted cash, and equivalents at beginning of period 8,691 — 1,003 9,694 Cash, restricted cash, and equivalents at end of period $ 8,021 $ — $ 1,385 $ 9,406 (1) See footnote (1) in table above. Reconciliation of Cash, Restricted Cash, and Equivalents — The following table reconciles cash, restricted cash, and equivalents per the consolidated statements of cash flows to the consolidated balance sheets. December 31, December 31, December 31, (in thousands) Balance Sheets Cash and cash equivalents $ 82,486 $ 76,649 $ 8,021 Cash and cash equivalents – restricted 46,888 73,657 — Other long-term assets 1,602 1,427 1,385 Statement of Cash Flows Cash, restricted cash, and equivalents $ 130,976 $ 151,733 $ 9,406 Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact December 2018 2018-20: Leases – (Topic 842) Narrow-Scope Improvements for Lessors The amendments in this ASU provide entities with additional guidance about the recognition of variable payments for contracts with lease and nonlease components. These amendments provide lessors the option to exclude certain lessor costs from recognition. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below November 2018 2018-19: Codification Improvements to Topic 326 – Financial Instruments – Credit Losses The amendments in this ASU make targeted improvements to the implementation guidance in ASU 2016-13. The amendments clarify that receivables arising from operating leases are not within the scope of ASC 326-20, but instead should be accounted for in accordance with Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2020, Modified retrospective Currently under evaluation, but not expected to be material August 2018 2018-15: Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract The amendments align the requirements for capitalizing implementation costs in a hosting arrangement with the guidance for internal-use software, resulting in expensing preliminary or post-implementation project costs and capitalizing certain application development costs. The capitalized costs should be included in the balance sheet line that includes prepayment for the fees of the associated hosting arrangement, and amortized over the noncancellable period of the arrangement. Amortization expense should be included in the income statement line that includes the fees associated with the hosting element of the arrangement. Payments for capitalized implementation costs should be classified in the statement of cash flows in the same manner as payments made for hosting element fees. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2020, Prospective Currently under evaluation, but not expected to be material August 2018 2018-13: Fair Value Measurement (Topic 820): Disclosure Framework – Change to the Disclosure Requirements for Fair Value Measurement The amendments in this ASU modify several disclosure requirements under Topic 820. These changes include removing the disclosure requirements related to the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, and adding disclosure requirements about the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Additionally, the amendments remove the phrase "at a minimum" from the codification clarifying that materiality should be considered when evaluating disclosure requirements. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. January 2019, Retrospective Not expected to be material (1) Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact July 2018 2018-11: Leases (Topic 842): Targeted Improvements The amendments in this ASU provide entities with an additional transition method for implementing ASC Topic 842, in which entities have the option to apply the new standard at the adoption date, recognizing a cumulative-effect adjustment to the opening balance of retained earnings. Comparative periods would not be restated, and would instead be presented under the legacy ASC Topic 840 guidance. Under certain conditions, the amendments in this ASU also provide lessors a practical expedient regarding separating nonlease components from the associated lease components if the nonlease components would otherwise be accounted for under ASC Topic 606, Revenue from Contracts with Customers. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below July 2018 2018-10: Leases (Topic 842): Codification Improvements This ASU contains various amendments to ASC Topic 842 that clarify the language, remove inconsistencies, and improve upon other issues, including those associated with implementing the new standard. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below June 2018 2018-07: Compensation – Improvements to Nonemployee Share-Based Payment Accounting The amendments in this ASU expand the scope of ASC Topic 718 to include share-based payments to nonemployees, and for public business entities include 1) measuring awards to nonemployees at grant-date fair value, 2) measuring awards to nonemployees at the grant date, 3) for awards with performance conditions granted to nonemployees, assessing the probability of satisfying performance conditions when measuring such awards, and 4) generally subjecting equity-classified awards to the requirements of ASC Topic 718, eliminating the requirement to reassess classification upon vesting. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. January 2019, Modified retrospective Currently under evaluation (2) January 2018 2018-01: Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842 The amendments in this ASU permit entities to elect to exclude land easements which were not previously recorded as leases from the evaluation related to the adoption of ASC Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. Refer to ASU 2016-02, below Refer to ASU 2016-02, below January 2017 2017-04: Intangibles – Goodwill and Other (Topic 350) Simplifying the Test for Goodwill Impairment The amendments in this ASU are intended to simplify subsequent measurement of goodwill. The key amendment in the ASU eliminates Step 2 from the goodwill impairment test, in which entities measured a goodwill impairment loss by comparing the implied fair value to the carrying amount of a reporting unit's goodwill. Instead, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value with the carrying amount of a reporting unit and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value. January 2020, prospective Currently under evaluation; not expected to be material Date Issued Reference Description Expected Adoption Date and Method Financial Statement Impact June 2016 2016-13: Financial Instruments – Credit Losses (Topic 326) – Measurement of Credit Losses on Financial Instruments The purpose of this ASU is to amend the current incurred loss impairment methodology with a new methodology that reflects expected credit losses and requires a broader range of reasonable and supportable information to inform credit loss estimates. This is the final credit accounting standard, out of a series, with detailed guidance on the new loss reserve model, Current Expected Credit Loss ("CECL"). Among other provisions, the amendments in the ASU require a financial asset (or group of assets) measured at amortized cost basis to be presented at the net amount expected to be collected. Entities are no longer required to wait until a loss is probable to record it. January 2020, Adoption method varies by amendment Currently under evaluation; not expected to be material February 2016 2016-02: Leases (Topic 842) The new standard requires lessees to recognize assets and liabilities arising from both operating and financing leases on the balance sheet. Lessor accounting for leases is largely unaffected. For public business entities, the new standard is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. January 2019, Modified retrospective - cumulative-effect adjustment to beginning balance of retained earnings at the adoption date Expected to be material (3) (1) ASU 2018-13: Fair Value Measurement (Topic 820): Disclosure Framework – Change to the Disclosure Requirements for Fair Value Measurement — Upon adoption, management expects to have fewer disclosures regarding its fair value measurements as a result of the amendments that eliminate "at a minimum" from the phrase, "an entity shall disclose at a minimum." The amendments are intended to allow entities to exercise discretion when considering fair value disclosures, including materiality considerations. Accordingly, the Company will exclude immaterial disclosures regarding fair value measurements from its quarterly and annual reports upon adoption, beginning in the first quarter of 2019. (2) ASU 2018-07: Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting — In accordance with the amendments in this ASU, the Company will be required to measure any nonemployee liability-classified awards that have not been settled by the adoption date and any equity-classified awards for which a measurement date has not been established through a cumulative-effect adjustment to retained earnings as of January 1, 2019. The Company is not expecting a material impact from adopting the amendments in this ASU, as the Company will have no unvested share-based payment awards related to its nonemployee directors as of January 1, 2019. (3) ASC 842, Leases — The Company established an implementation team, which includes support from external experts, to transition the Company from accounting for leases under ASC 840 to accounting for leases under ASC 842. The diagnostic phase of implementing the new standard is complete, and management has selected practical expedients and accounting policies to evaluate the lease population. The Company is substantially complete with the process of extracting and uploading lease data available from existing systems and documents into its new lease software solution. Management expects to elect the package of practical expedients (regarding lease identification, lease classification, and initial direct costs), but not the hindsight practical expedient. Additionally, management expects to elect accounting policies to account for its revenue equipment leases at the portfolio level, to bundle nonlease components with their related lease components (as lessee), and to not recognize a right-of-use asset or lease liability for short-term leases. These policies are not substantially different from the Company’s current accounting policies. After considering the above practical expedient and accounting policy elections, management expects that adopting the new lease standard will result in adding right-of-use assets of $270.0 million to $300.0 million and corresponding lease liabilities of $270.0 million to $300.0 million to the consolidated balance sheet as of January 1, 2019, with the net impact being recorded as a cumulative-effect adjustment to retained earnings, as applicable. The impact of adopting the new lease standard is not expected to be material to the Company’s consolidated income statement, liquidity, or compliance with debt covenants. Since management is continuing to evaluate the impacts of the above standards, disclosures around these preliminary assessments are subject to change.

Merger and Acquisition Merger_2

Merger and Acquisition Merger and Acquisition (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
2017 Merger - fair value consideration transferred	The following table summarizes the total fair value consideration transferred: (In thousands, except ratio and stock price) Number of Swift shares outstanding at September 8, 2017 134,765 Swift share consolidation ratio 0.72 Swift shares outstanding post-Reverse Split and immediately prior to the 2017 Merger 97,031 Closing price of Knight on September 8, 2017 $ 40.85 Fair value of equity portion of the 2017 Merger consideration $ 3,963,712 Fair value of Swift equity awards and noncontrolling interest assumed 13,193 Total fair value of consideration transferred $ 3,976,905
2017 Merger allocation of purchase consideration	The following is a summary of the allocation of purchase consideration to the estimated fair value of Swift's assets acquired and liabilities assumed in the 2017 Merger: September 9, 2017 Opening Balance Sheet as Reported at September 30, 2017 Adjustments Adjusted September 9, 2017 Opening Balance Sheet as reported at December 31, 2018 (In thousands) Fair value of the consideration transferred $ 3,976,905 $ — $ 3,976,905 Cash and cash equivalents $ 28,484 $ — $ 28,484 Restricted cash and fixed maturity securities 85,615 — 85,615 Trade and other receivables 411,767 — 411,767 Prepaid expenses 44,564 — 44,564 Other current assets 19,736 — 19,736 Property and equipment 1,522,123 — 1,522,123 Identifiable intangible assets (1) 1,285,900 165,800 1,451,700 Other noncurrent assets 18,537 — 18,537 Total assets 3,416,726 165,800 3,582,526 Accounts payable (188,411 ) — (188,411 ) Accrued liabilities (2) (232,280 ) (6,466 ) (238,746 ) Claims accruals (306,846 ) — (306,846 ) Long-term debt and capital lease obligations (894,681 ) — (894,681 ) Deferred tax liabilities (1) (2) (741,405 ) (61,900 ) (803,305 ) Other long-term liabilities (18,452 ) — (18,452 ) Total liabilities (2,382,075 ) (68,366 ) (2,450,441 ) Goodwill (1) (2) $ 2,942,254 $ (97,434 ) $ 2,844,820 (1) Adjustments made to identifiable intangible assets, goodwill, and deferred tax liabilities pertain to management's re-evaluation of the royalty rate used associated with certain trade names. The following table summarizes the fair value of the consideration transferred as of the acquisition date, including any adjustments during the measurement period: March 16, 2018 Opening Balance Sheet as Reported at March 31, 2018 Adjustments Adjusted March 16, 2018 Opening Balance Sheet as Reported at December 31, 2018 (in thousands) Fair value of the consideration transferred $ 103,223 $ 124 $ 103,347 Cash 1,654 — 1,654 Trade receivables 11,745 1,265 13,010 Other assets 7,785 842 8,627 Property and equipment 41,403 — 41,403 Identifiable intangible assets (1) 23,000 (400 ) 22,600 Total assets 85,587 1,707 87,294 Accounts payable 1,959 1,577 3,536 Accrued liabilities 2,419 4,942 7,361 Claims accruals 230 172 402 Total liabilities 4,608 6,691 11,299 Goodwill $ 22,244 $ 5,108 $ 27,352 (1) Includes a $17.9 million customer relationship and a $4.7 million trade name.
2017 Merger Intangible Assets	The estimated fair value of the acquired identifiable intangible assets is based on a valuation completed for Swift, along with related tangible assets, using a combination of the income method and comparable market transactions. Following are the details of the preliminary purchase price allocated to the identifiable intangible assets acquired: Estimated Life Estimated Fair Value as of September 9, 2017 Adjustments (1) Adjusted Estimated Fair Value as of September 9, 2017 (years) (thousands) Customer relationships 10 - 20 years $ 817,200 $ (700 ) $ 816,500 Trade name indefinite 468,700 166,500 635,200 Total identifiable intangible assets $ 1,285,900 $ 165,800 $ 1,451,700
2017 Merger Pro-forma information	2018 2017 (in thousands, except per share data) Total revenue $ 5,366,551 $ 5,230,674 Net income attributable to Knight-Swift $ 419,812 $ 536,062 Diluted earnings per share $ 2.36 $ 3.00

Marketable Securities Marketa_2

Marketable Securities Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2018
Marketable Securities [Abstract]
Realized gains from available-for-sale securities	The following table shows realized gains during 2018 , 2017 , and 2016 , on certain securities that were classified as available-for-sale: 2018 2017 2016 (In thousands) Realized Gains: Sales proceeds $ — $ — $ 7,403 Cost of securities sold — — 2,909 Realized gain $ — $ — $ 4,494 Realized gain, net of taxes $ — $ — $ 2,771

Restricted Investments, Held-_2

Restricted Investments, Held-to-Maturity (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Gross Unrealized Gains And Losses, Estimated Fair Value Of Fixed Maturity Securities	The following table presents the cost or amortized cost, gross unrealized gains and temporary losses, and estimated fair value of the Company's restricted investments: December 31, 2018 Gross Unrealized Cost or Amortized Cost Gains Temporary Estimated Fair Value (In thousands) US corporate securities $ 15,296 $ 1 $ (16 ) $ 15,281 Municipal bonds 1,082 — — 1,082 Negotiable certificates of deposit 1,035 — — 1,035 Restricted investments, held-to-maturity $ 17,413 $ 1 $ (16 ) $ 17,398 December 31, 2017 Gross Unrealized Cost or Amortized Cost Gains Temporary Estimated Fair Value (In thousands) US corporate securities $ 15,982 $ — $ (14 ) $ 15,968 Municipal bonds 4,970 — (10 ) 4,960 Negotiable certificates of deposit 1,280 — — 1,280 Restricted investments, held-to-maturity $ 22,232 $ — $ (24 ) $ 22,208

Transportation Resource Partn_2

Transportation Resource Partners Transportation Resource Partners (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Transportation Resource Partners Investments and Commitments	The following table presents ownership and commitment information for Knight's investments in TRP partnerships: December 31, 2018 Knight's Ownership Interest (5) Total Commitment (All Partners) Knight's Contracted Commitment Knight's Remaining Commitment (Dollars in thousands) TRP – equity investment (1) 2.3 % $ 260,000 $ 5,500 $ — TRP III – equity method investment (2) 5.3 % $ 245,000 $ 15,000 $ 1,715 TRP IV – equity investment (3) (1) 4.1 % $ 116,000 $ 4,900 $ 2,002 TRP Coinvestment NTI – equity method investment (4) 8.3 % $ 120,000 $ 10,000 $ — TRP Coinvestment QLS – equity method investment (4) 25.0 % $ 39,000 $ 9,735 $ — (1) In accordance with ASC 321, Investments – Equity Securities , these investments are recorded at cost minus impairment. (2) Management anticipates that the following amounts will be due: $1.7 million from 2020 through 2021. (3) Management anticipates that the following amounts will be due: $1.0 million in 2019, $0.2 million from 2020 through 2021, $0.2 million from 2022 through 2023, and $0.6 million from 2024 through 2025. (4) The TRP Coinvestments are unconsolidated majority interests. Management considered the criteria set forth in ASC 323, Investments – Equity Method and Joint Ventures , to establish the appropriate accounting treatment for these investments. This guidance requires the use of the equity method for recording investments in limited partnerships where the "so minor" interest is not met. As such, the investments are being accounted for under the equity method. Knight's ownership interest reflects its ultimate ownership of the portfolio companies underlying the TRP Coinvestment NTI and TRP Coinvestment QLS legal entities. (5) Knight's share of the results is included within "Other income, net" in the consolidated income statements.
Transportation Resources Partners Carrying Value	Net investment balances included in "Other long-term assets" in the consolidated balance sheets were as follows: December 31, 2018 2017 (in thousands) TRP – equity investment (1) $ 211 $ 211 TRP III – equity method investment 1,781 1,973 TRP IV – equity investment (1) 2,022 2,577 TRP Coinvestment NTI – equity method investment 5,547 7,579 TRP Coinvestment QLS – equity method investment 11,085 8,054 Total carrying value $ 20,646 $ 20,394 (1) In accordance with ASC 321, Investments – Equity Securities , these investments are recorded at cost minus impairment.

Trade Receivables, net (Tables)

Trade Receivables, net (Tables)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Schedule of Trade Receivables, net	Trade receivables balances were as follows: December 31, 2018 2017 (In thousands) Trade customers $ 597,077 $ 565,732 Equipment manufacturers 7,166 6,017 Other 28,942 17,345 Trade receivables 633,185 589,094 Less: Allowance for doubtful accounts (16,355 ) (14,829 ) Trade receivables, net (1) $ 616,830 $ 574,265 (1) Includes $15.6 million of in-transit revenue as of December 31, 2018 . The following is a rollforward of the allowance for doubtful accounts for trade receivables: 2018 2017 2016 (In thousands) Beginning balance $ 14,829 $ 2,727 $ 3,106 (Reduction) provision (3,092 ) 4,671 909 Write-offs directly against the reserve (1,362 ) (1,583 ) — Write-offs for revenue adjustments 5,861 (3,758 ) (1,288 ) Other (1) 119 12,772 — Ending balance $ 16,355 $ 14,829 $ 2,727 (1) Increase in allowance for doubtful accounts relates to trade receivables assumed in 2017 from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions. Notes receivable are included in "Other current assets" and "Other long-term assets" in the consolidated balance sheets and were comprised of: December 31, 2018 2017 (In thousands) Notes receivable from independent contractors $ 9,318 $ 8,977 Notes receivable from third parties 7,075 7,865 Gross notes receivable 16,393 16,842 Allowance for doubtful notes receivable (1,051 ) (1,040 ) Total notes receivable, net of allowance $ 15,342 $ 15,802 Current portion, net of allowance 4,563 4,742 Long-term portion $ 10,779 $ 11,060 The following is a rollforward of the allowance for doubtful notes receivable: December 31, 2018 2017 2016 (In thousands) Beginning balance $ 1,040 $ 240 $ 273 (Reduction) provision (100 ) 574 (27 ) Write-offs (103 ) (53 ) (6 ) Other (1) 214 279 — Ending balance $ 1,051 $ 1,040 $ 240 (1) Increase in allowance for doubtful notes relates to notes receivable in 2017 assumed from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions. The following is a rollforward of the allowance for doubtful notes receivable: December 31, 2018 2017 2016 (In thousands) Beginning balance $ 1,040 $ 240 $ 273 (Reduction) provision (100 ) 574 (27 ) Write-offs (103 ) (53 ) (6 ) Other (1) 214 279 — Ending balance $ 1,051 $ 1,040 $ 240 (1) Increase in allowance for doubtful notes relates to notes receivable in 2017 assumed from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions.

Notes Receivable, net (Tables)

Notes Receivable, net (Tables)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Schedule of Notes Receivable	Trade receivables balances were as follows: December 31, 2018 2017 (In thousands) Trade customers $ 597,077 $ 565,732 Equipment manufacturers 7,166 6,017 Other 28,942 17,345 Trade receivables 633,185 589,094 Less: Allowance for doubtful accounts (16,355 ) (14,829 ) Trade receivables, net (1) $ 616,830 $ 574,265 (1) Includes $15.6 million of in-transit revenue as of December 31, 2018 . The following is a rollforward of the allowance for doubtful accounts for trade receivables: 2018 2017 2016 (In thousands) Beginning balance $ 14,829 $ 2,727 $ 3,106 (Reduction) provision (3,092 ) 4,671 909 Write-offs directly against the reserve (1,362 ) (1,583 ) — Write-offs for revenue adjustments 5,861 (3,758 ) (1,288 ) Other (1) 119 12,772 — Ending balance $ 16,355 $ 14,829 $ 2,727 (1) Increase in allowance for doubtful accounts relates to trade receivables assumed in 2017 from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions. Notes receivable are included in "Other current assets" and "Other long-term assets" in the consolidated balance sheets and were comprised of: December 31, 2018 2017 (In thousands) Notes receivable from independent contractors $ 9,318 $ 8,977 Notes receivable from third parties 7,075 7,865 Gross notes receivable 16,393 16,842 Allowance for doubtful notes receivable (1,051 ) (1,040 ) Total notes receivable, net of allowance $ 15,342 $ 15,802 Current portion, net of allowance 4,563 4,742 Long-term portion $ 10,779 $ 11,060 The following is a rollforward of the allowance for doubtful notes receivable: December 31, 2018 2017 2016 (In thousands) Beginning balance $ 1,040 $ 240 $ 273 (Reduction) provision (100 ) 574 (27 ) Write-offs (103 ) (53 ) (6 ) Other (1) 214 279 — Ending balance $ 1,051 $ 1,040 $ 240 (1) Increase in allowance for doubtful notes relates to notes receivable in 2017 assumed from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions. The following is a rollforward of the allowance for doubtful notes receivable: December 31, 2018 2017 2016 (In thousands) Beginning balance $ 1,040 $ 240 $ 273 (Reduction) provision (100 ) 574 (27 ) Write-offs (103 ) (53 ) (6 ) Other (1) 214 279 — Ending balance $ 1,051 $ 1,040 $ 240 (1) Increase in allowance for doubtful notes relates to notes receivable in 2017 assumed from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions.

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of goodwill	The changes in the carrying amounts of goodwill were as follows: December 31, 2018 2017 (In thousands) Goodwill at beginning of period $ 2,887,867 $ 47,031 Amortization relating to deferred tax assets (17 ) (10 ) Abilene Acquisition (1) 27,352 — Goodwill related to 2017 Merger (2) 3,974 2,840,846 Goodwill at end of period $ 2,919,176 $ 2,887,867 (1) The goodwill associated with the Abilene Acquisition was allocated to the Knight Trucking segment. See Note 5 regarding the amount attributed to adjustments to the March 17, 2018 opening balance sheet. (2) The goodwill adjustment associated with the 2017 Merger resulted in a $4.8 million increase, a $1.1 million increase, and a $1.9 million decrease in goodwill allocated to the Swift Truckload, Swift Dedicated, and Swift Refrigerated segments, respectively. See Note 5 regarding the nature of the adjustment. The following presents the components of goodwill by segment as of December 31, 2018 and 2017 : December 31, 2018 2017 Net Carrying Amount (1) Net Carrying Amount (1) (In thousands) Swift – Truckload $ 1,154,783 $ 1,150,012 Swift – Dedicated 780,392 779,335 Swift – Refrigerated 648,759 650,613 Swift – Intermodal 175,594 175,594 Swift – Non-reportable 85,292 85,292 Knight – Trucking 74,356 47,021 Goodwill $ 2,919,176 $ 2,887,867 (1) Except for the net accumulated amortization related to deferred tax assets in the Knight Trucking segment, the net carrying amount and gross carrying amount are equal since there are no accumulated impairment losses.
Schedule of Intangible Assets, net	Other intangible asset balances were as follows: December 31, 2018 2017 (In thousands) Customer relationships and non-compete: Gross carrying amount (1) $ 838,100 $ 820,200 Accumulated amortization (57,081 ) (14,497 ) Customer relationships and non-compete, net 781,019 805,703 Trade names: Gross carrying amount (1) 639,900 635,200 Intangible assets, net $ 1,420,919 $ 1,440,903 (1) The changes in the gross carrying amounts of intangible assets are related to the Abilene Acquisition and are discussed in Note 5 .
Finite-lived Intangible Assets Amortization Expense	The following table presents amortization of intangible assets related to the 2017 Merger and intangible assets existing prior to the 2017 Merger: 2018 2017 2016 (In thousands) Amortization of intangible assets related to the 2017 Merger $ 41,375 $ 12,872 $ — Amortization related to other intangible assets 1,209 500 500 Amortization of intangibles $ 42,584 $ 13,372 $ 500

Accrued Payroll and Purchased_2

Accrued Payroll and Purchased Transportation and Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Accrued Liabilities [Abstract]
Schedule of Accrued Payroll and Purchased Transportation	The following table presents the composition of accrued payroll and purchased transportation: December 31, 2018 2017 (In thousands) Accrued payroll (1) $ 68,121 $ 58,438 Accrued purchased transportation 58,343 48,579 Accrued payroll and purchased transportation $ 126,464 $ 107,017 (1) Accrued payroll includes accruals related to the various 401(k) plans the Company offers to its employees. In order to qualify for these plans, employees must meet the minimum age requirement ( 18 – 21 years) and have completed six months to one year of service with the Company. Employees' rights to employer contributions are fully vested after five to 6 years from their date of employment. The plans offer discretionary matching contributions capped at either $1,600 annually per employee or 3% of an employee's compensation. The Company's employee benefits expense for matching contributions related to the 401(k) plans was approximately $8.7 million , $3.9 million , and $1.2 million in 2018 , 2017 , and 2016 , respectively. This expense was included in "Salaries, wages, and benefits" in the consolidated income statements. As of December 31, 2018 and 2017 , the balance included $6.4 million and $6.8 million , respectively, in respect to matching contributions for the 401(k) plans.
Schedule of Accrued Liabilities	The following table presents the composition of accrued liabilities: December 31, 2018 2017 (In thousands) Accrued legal (1) 90,789 121,453 Other 60,711 64,926 Accrued liabilities $ 151,500 $ 186,379 (1) See Note 20 for further details regarding the Company's legal accruals.

Claims Accruals (Tables)

Claims Accruals (Tables)	12 Months Ended
	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Abstract]
Schedule of Claims Accruals	Claims accruals were comprised of the following: December 31, 2018 2017 (In thousands) Auto reserves $ 222,004 $ 204,400 Workers’ compensation reserves 120,522 126,563 Independent contractor claims reserves 12,170 15,236 Cargo damage reserves 2,998 4,047 Employee medical reserves 3,677 3,183 Claims accruals 361,371 353,429 Less: current portion of claims accruals (160,044 ) (147,285 ) Claims accruals, less current portion $ 201,327 $ 206,144

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Tax Expense (Benefit)	The following table presents the Company's income tax expense: 2018 2017 2016 (In thousands) Current expense: Federal $ 44,357 $ 4,868 $ 43,638 State 22,300 8,337 8,500 Foreign 3,124 133 — 69,781 13,338 52,138 Deferred expense (benefit): Federal 59,508 (323,326 ) 6,789 State 1,639 17,731 (1,335 ) Foreign 461 541 — 61,608 (305,054 ) 5,454 Income tax expense (benefit) $ 131,389 $ (291,716 ) $ 57,592
Schedule Of Effective Income Tax Rate Reconciliation	Actual tax expense differs from expected tax expense as follows: 2018 2017 2016 (In thousands) Computed "expected" tax expense $ 117,478 $ 67,798 $ 53,490 Increase (decrease) in income taxes resulting from: State income taxes, net of federal income tax benefit 19,256 4,871 4,657 Statutory rate change effect on deferred taxes 452 (367,000 ) — Other (5,797 ) 2,615 (555 ) Income tax expense (benefit) $ 131,389 $ (291,716 ) $ 57,592
Components Of Net Deferred Tax Asset (Liability)	The components of the net deferred tax asset (liability) included in "Deferred tax liabilities" in the consolidated balance sheets were: December 31, 2018 2017 (In thousands) Deferred tax assets: Claims accrual $ 79,675 $ 70,564 Allowance for doubtful accounts 5,333 5,117 Amortization of stock options 5,325 4,717 Accrued liabilities 27,692 37,654 Vacation accrual 3,499 3,585 Other 8,759 7,227 Total deferred tax assets 130,283 128,864 Valuation allowance — — Total deferred tax assets, net 130,283 128,864 Deferred tax liabilities: Property and equipment, principally due to differences in depreciation (503,570 ) (429,917 ) Prepaid taxes, licenses, and permits deducted for tax purposes (10,933 ) (10,217 ) Intangible assets (354,944 ) (365,564 ) Other (374 ) (2,243 ) Deferred tax liabilities (869,821 ) (807,941 ) Deferred income taxes $ (739,538 ) $ (679,077 )
Reconciliation Of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amounts of unrecognized tax benefits for 2018, 2017, and 2016 is as follows: 2018 2017 2016 (In thousands) Unrecognized tax benefits at beginning of year $ 7,096 $ 729 $ — Increases for tax positions taken prior to beginning of year 1,056 5,432 729 Increases for tax positions taken in the current year — 935 — Decreases for tax positions taken prior to beginning of year (729 ) — — Unrecognized tax benefits at end of year $ 7,423 $ 7,096 $ 729

Accounts Receivable Securitiz_2

Accounts Receivable Securitization (Tables)	12 Months Ended
	Dec. 31, 2018
Transfers and Servicing of Financial Assets [Abstract]
Accounts Receivable Securitization [Table Text Block]	The following table summarizes the key differences between the 2018 RSA and 2015 RSA: 2018 RSA 2015 RSA (Dollars in thousands) Effective July 11, 2018 December 10, 2015 Final maturity date July 9, 2021 January 10, 2019 Borrowing capacity $325,000 $400,000 Accordion option (1) $175,000 $75,000 Unused commitment fee rate (2) 20 to 40 basis points 35 basis points Program fees on outstanding balances (3) one month LIBOR + 80 to 100 basis points one-month LIBOR + 90 basis points (1) The accordion option increases the maximum borrowing capacity, subject to participation by the purchasers. (2) The 2018 RSA commitment fee rate is based on the percentage of the maximum borrowing capacity utilized. (3) The 2018 RSA program fee is based on the Company's consolidated total net leverage ratio. The 2018 RSA and 2015 RSA are secured borrowings that are collateralized by the Company's eligible receivables, for which the Company is the servicing agent. The Company's eligible receivables are included in "Trade receivables, net of allowance for doubtful accounts" in the consolidated balance sheets. As of December 31, 2018 , the Company's eligible receivables generally have high credit quality, as determined by the obligor's corporate credit rating. Availability under the 2018 RSA and 2015 RSA is calculated as follows: 2018 RSA 2015 RSA December 31, December 31, (In thousands) Borrowing base, based on eligible receivables $ 325,000 $ 317,600 Less: outstanding borrowings (1) (240,000 ) (305,000 ) Less: outstanding letters of credit (70,900 ) — Availability under accounts receivable securitization facilities $ 14,100 $ 12,600 (1) Outstanding borrowings are included in "Accounts receivable securitization" in the consolidated balance sheets. Interest accrued on the aggregate principal balance at a rate of 3.2% and 2.1% , as of December 31, 2018 and 2017 , respectively.

Debt And Financing (Tables)

Debt And Financing (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Debt Balances by Instrument [Table Text Block]	Other than the Company's accounts receivable securitization as discussed in Note 16 and its outstanding capital lease obligations as discussed in Note 18 , the Company's long-term debt consisted of the following: December 31, 2018 2017 (In thousands) Term Loan, due October 2020, net (1) (2) $ 364,590 $ 364,355 Other long-term debt, including current portion 421 446 Total long-term debt, including current portion 365,011 364,801 Less: current portion of long-term debt (421 ) (30 ) Long-term debt, less current portion $ 364,590 $ 364,771 December 31, 2018 2017 (In thousands) Total long-term debt, including current portion $ 365,011 $ 364,801 Revolver, due October 2022 (1) (3) 195,000 125,000 Long-term debt, including revolving line of credit $ 560,011 $ 489,801 (1) Refer to Note 24 for information regarding the fair value of debt. (2) Net of $0.4 million and $0.6 million deferred loan costs at December 31, 2018 and 2017 , respectively. (3) The Company also had outstanding letters of credit under the Revolver, primarily related to workers' compensation and self-insurance liabilities of $36.6 million and $153.6 million at December 31, 2018 and 2017 , respectively.
Schedule of Debt Terms [Table Text Block]	The following table presents the key terms of the 2017 Debt Agreement: Term Loan Revolver (2) 2017 Debt Agreement Terms: (Dollars in thousands) Maximum borrowing capacity $400,000 $800,000 Final maturity date October 2, 2020 October 3, 2022 Interest rate base LIBOR LIBOR Interest rate minimum margin (1) 0.88% 0.88% Interest rate maximum margin (1) 1.50% 1.50% Minimum principal payment — amount $— $— Minimum principal payment — frequency Once Once Minimum principal payment — commencement date October 2, October 3, (1) The interest rate margin for the Term Loan and Revolver is based on the Company's consolidated leverage ratio. As of December 31, 2018 , interest accrued at 3.522% on the Term Loan and 3.448% on the Revolver. As of December 31, 2017 interested accrued at 2.694% on the Term Loan and 2.687% on the Revolver. (2) The commitment fee for the unused portion of the Revolver is based on the Company's consolidated leverage ratio, and ranges from 0.07% to 0.20% . As of December 31, 2018 , commitment fees on the unused portion of the Revolver accrued at 0.100% and outstanding letter of credit fees accrued at 1.000% . As of December 31, 2017 , commitment fees on the unused portion of the Revolver accrued at 0.125% and outstanding letter of credit fees accrued at 1.125% .

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2018
Leases [Abstract]
Schedule of future minimum lease commitments [Table Text Block]	As of December 31, 2018 , annual future minimum lease payments for all noncancelable leases were: Operating Capital (In thousands) 2019 $ 123,380 $ 61,285 2020 79,088 15,843 2021 42,441 30,845 2022 24,693 18,528 2023 11,728 1,347 Thereafter 25,403 9,572 Future minimum lease payments $ 306,733 $ 137,420 Less: amounts representing interest (7,921 ) Present value of minimum lease payments 129,499 Less: current portion (58,251 ) Capital lease obligations – less current portion $ 71,248
Schedule of future minimum lease payments receivable [Table Text Block]	Annual future minimum lease payments receivable under operating leases for the periods noted below were: (In thousands) 2019 $ 54,080 2020 37,694 2021 22,991 2022 8,343 2023 13 Thereafter — Future minimum lease payments receivable $ 123,121

Contingencies and Legal Proce_2

Contingencies and Legal Proceedings (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Loss Contingencies by Contingency [Table Text Block]	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 consolidated balance sheets. The Company has recorded an aggregate accrual of approximately $90.8 million and $121.5 million relating to the Company's outstanding legal proceedings as of December 31, 2018 and 2017 , respectively. 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 Washington Overtime Class Actions The plaintiffs allege one or more of the following, pertaining to Washington state-based driving associates: that Swift 1) failed to pay minimum wage; 2) failed to pay overtime; 3) failed to pay all wages due at established pay periods; 4) failed to provide proper meal and rest periods; 5) failed to provide accurate wage statements; and 6) unlawfully deducted from employee wages. The plaintiffs seek unpaid wages, exemplary damages, interest, other costs, and attorneys’ fees. Plaintiff(s) Defendant(s) Date instituted Court or agency currently pending in Troy Slack (1) Swift Transportation Company of Arizona, LLC and Swift Transportation Corporation September 9, 2011 United States District Court for the Western District of Washington Julie Hedglin (1) Swift Transportation Company of Arizona, LLC and Swift Transportation Corporation January 14, 2016 United States District Court for the Western District of Washington Recent Developments and Current Status The parties in the Slack matter have reached a final settlement. Additionally, the parties in the Hedglin matter have reached a final settlement. The likelihood that a loss has been incurred for the Slack and Hedglin matters is probable and estimable, and the loss has accordingly been accrued. 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 The parties have reached a tentative settlement of the matter. As such, the likelihood that a loss has been incurred is probable and estimable, and the loss has accordingly been accrued. (1) Individually and on behalf of all others similarly situated. INDEPENDENT CONTRACTOR MATTERS Ninth Circuit Independent Contractors Misclassification Class Action The putative class alleges that Swift misclassified independent contractors as independent contractors, instead of employees, in violation of the FLSA 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 2017, the district court issued an order finding that the plaintiffs had signed contracts of employment and thus the case could properly proceed in court, instead of arbitration. In February 2019, the parties reached a tentative settlement pending approval by the court. Based on the above, the likelihood that a loss has been incurred is probable and estimable, and the loss has accordingly been accrued. Utah Collective and Individual Arbitration The plaintiffs allege that the Central Parties (defined below) misclassified independent contractors as independent contractors, instead of employees, in violation of the FLSA and various state laws. 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 Gabriel Ciluffo, Kevin Shire, and Bryan Ratterree (1) Central Refrigerated Service, Inc., Central Leasing, Inc., Jon Isaacson, and Jerry Moyes (the "Central Parties"), as well as Swift Transportation Company June 1, 2012 American Arbitration Association Recent Developments and Current Status In October 2016, the arbitrator ruled that approximately 1,300 Central Refrigerated Service, Inc. drivers should have been classified as employees, not independent contractors. The arbitrator ruled that damages could ultimately be assessed in a collective proceeding and denied Swift's motion to decertify the collective proceeding. On April 14, 2017, the parties reached a settlement of the matter. On April 3, 2018, the court granted final approval of the settlement and the Company paid the settlement in the second quarter of 2018. (1) Individually and on behalf of all others similarly situated.

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Compensation Expense Related To Stock-Based Compensation	Stock-based compensation expense, net of forfeitures, which is included in "Salaries, wages, and benefits" in the consolidated income statements is comprised of the following: 2018 2017 2016 (In thousands) Stock options $ 1,678 $ 1,788 $ 1,734 Restricted stock units and restricted stock awards 8,019 4,004 1,506 Performance units 1,791 450 801 Stock-based compensation expense – equity awards $ 11,488 $ 6,242 $ 4,041 Stock-based compensation expense – liability awards (1) 899 148 — Total stock-based compensation expense, net of forfeitures 12,387 6,390 4,041 Income tax benefit $ 3,097 $ 2,415 $ 1,515 (1) Includes awards granted to executive management in November 2017 and November 2018 that ultimately settle in cash upon fulfilling a requisite service period (for restricted stock units) and fulfilling a requisite service period and achieving performance targets (for performance units).
Schedule of Unrecognized Compensation Cost, Nonvested Awards [Table Text Block]	The following table presents the total unrecognized stock-based compensation expense and the expected weighted average period over which these expenses will be recognized: December 31, 2018 Expense Weighted Average Period (In thousands) (In years) Equity awards – Stock options $ 2,092 1.4 Equity awards – Restricted stock units and restricted stock awards 23,803 2.2 Equity awards – Performance units 3,763 2.8 Liability awards – Restricted stock units and performance units 3,067 2.4 Total unrecognized stock-based compensation expense $ 32,725 2.3
Schedule of Grants of Restricted Stock [Table Text Block]	Stock Award Grants 2018 2017 2016 Stock options — 497,421 569,480 Restricted stock units and restricted stock awards 420,014 266,958 17,000 Performance units 106,785 44,244 177,741 Equity awards granted 526,799 808,623 764,221 Liability awards granted (1) (2) 91,268 77,620 — Total stock awards granted 618,067 886,243 764,221 (1) Includes 54,761 and 46,572 performance units in 2018 and 2017 , respectively. (2) Includes 36,507 and 31,048 restricted stock units in 2018 and 2017 , respectively.
Summary Of Activity Related To Stock Options	A summary of 2018 stock option activity follows: Stock options outstanding: Shares Under Option Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (1) (In years) (In thousands) Stock options outstanding at December 31, 2017 1,959,291 $ 25.48 3.2 $ 35,779 Granted — — Exercised (2) (533,226 ) 20.56 Expired (26,163 ) 28.72 Forfeited (78,297 ) 30.17 Stock options outstanding at December 31, 2018 1,321,605 $ 27.13 2.6 $ 2,690 Aggregate number of stock options expected to vest at a future date as of December 31, 2018 558,184 $ 29.71 2.7 $ 160 Exercisable at December 31, 2018 739,264 $ 25.02 2.6 $ 2,527 (1) The aggregate intrinsic value was computed using the closing share price on December 31, 2018 of $25.07 and on December 29, 2017 of $43.72 , as applicable. (2) Includes 3,044 swapped shares which were excluded from the "Common stock issued to employees" activity on the Consolidated Statements of Stockholders' Equity.
Weighted Average Assumptions	The following table presents the weighted average assumptions used in the fair value computation: Stock option fair value assumptions: 2017 2016 Dividend yield (1) 0.72% 0.99% Risk-free rate of return (2) 1.49% 0.90% Expected volatility (3) 27.95% 27.91% Expected term (in years) (4) 3.2 2.7 Weighted average fair value of stock options granted $6.78 $4.28 (1) The dividend yield assumption is based on Knight's historical experience and anticipated future dividend payouts. (2) The risk-free interest rate assumption is based on the US Treasury securities at a constant maturity with a maturity period that most closely resembles the expected term of the stock option award. (3) Expected volatility of the Company's common stock is determined based on Knight's historical data. (4) The expected term of employee stock options represents the weighted-average period the stock options are expected to remain outstanding and was determined based on an analysis of historical exercise behavior.
Summary Of Exercise Of Stock Options	The following table summarizes stock option exercise information for the years presented: Stock option exercises 2018 2017 2016 (In thousands, except share data) Number of stock options exercised 533,226 589,020 708,244 Intrinsic value of stock options exercised $ 11,745 $ 8,792 $ 7,100 Cash received upon exercise of stock options $ 10,815 $ 13,159 $ 13,188 Income tax benefit $ 1,685 $ 1,833 $ 1,847
Rollforward of Company's Nonvested Stock Options	The following table is a rollforward of the Company's unvested stock options: Unvested stock options: Shares Weighted Average Fair Value Unvested stock options at December 31, 2017 1,040,697 $ 5.49 Granted — — Vested (380,059 ) 5.14 Forfeited (78,297 ) 5.76 Unvested stock options at December 31, 2018 582,341 $ 5.69
Rollforward of Nonvested Restricted Stock Awards [Table Text Block]	The following table is a rollforward of unvested restricted stock units, including restricted stock units classified as equity and those classified as liabilities: Unvested restricted stock units: Number of Awards Weighted Average Fair Value (1) Unvested restricted stock units at December 31, 2017 979,717 $ 26.59 Granted 456,521 38.07 Vested (2) (193,502 ) 24.43 Forfeited (72,762 ) 37.98 Unvested restricted stock units at December 31, 2018 1,169,974 $ 30.14 (1) The fair value of each restricted stock unit is based on the closing market price on the grant date. (2) Includes 53,274 of shares withheld for taxes which were excluded from the "Common stock issued to employees" activity on the Consolidated Statements of Stockholders' Equity.
Rollforward of Nonvested Performance Shares [Table Text Block]	The following table is a rollforward of unvested performance units, including performance units classified as equity and those classified as liabilities: Unvested performance units: Shares Weighted Average Fair Value Unvested performance units at December 31, 2017 147,633 $ 35.34 Granted 161,546 $ 34.34 Shares earned above target — $ — Vested — $ — Forfeited — $ — Unvested performance units at December 31, 2018 (1) 309,179 $ 29.50 (1) The performance measurement period for performance units granted in 2017 is January 1, 2018 to December 31, 2020 (three full calendar years). These awards will vest one month following the expiration of the performance measurement period. The performance measurement period for performance units granted in 2018 is January 1, 2019 to December 31, 2021 (three full calendar years). These awards will vest one month following the expiration of the performance measurement period
Performance unit fair value assumptions	The following table presents the weighted average assumptions used in the fair value computation for performance units, including performance units classified as equity and those classified as liabilities: Performance unit fair value assumptions: 2018 2017 2016 Dividend yield (1) 0.81 % 0.59 % 0.99 % Expected volatility (2) 32.30 % 31.28 % 27.95 % Average peer volatility (2) 28.61 % 28.45 % 34.37 % Average peer correlation coefficient (3) 0.58 0.60 0.60 Risk-free interest rate (4) 2.80 % 1.88 % 0.89 % Expected term (in years) (5) 3.1 3.1 2.8 Weighted-average fair value of performance units granted $ 34.34 $ 40.81 $ 23.89 (1) The dividend yield, used to project stock price to the end of the performance period, is based on the Knight's historical experience and future expectation of dividend payouts. Total stockholder return is determined assuming that dividends are reinvested in the issuing entity over the performance period, which is mathematically equivalent to utilizing a 0% dividend yield. (2) Management (or peer company) estimated volatility using Knight's (or peer company's) historical share price performance over the remaining performance period as of the grant date. (3) The correlation coefficients are used to model the way in which each entity tends to move in relation to each other; the correlation assumptions were developed using the same stock price data as the volatility assumptions. (4) The risk-free interest rate assumption is based on US Treasury securities at a constant maturity with a maturity period that most closely resembles the expected term of the performance award. (5) Since the Monte Carlo Simulation valuation is an open form model that uses an expected life commensurate with the performance period, the expected life of the performance units was assumed to be the period from the grant date to the end of the performance period.

Weighted Average Shares Outst_2

Weighted Average Shares Outstanding (Tables)	12 Months Ended
	Dec. 31, 2018
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: December 31, 2018 2017 2016 (In thousands) Basic weighted average common shares outstanding 177,018 110,657 80,362 Dilutive effect of equity awards 981 1,040 866 Diluted weighted average common shares outstanding 177,999 111,697 81,228 Anti-dilutive shares excluded from diluted earnings per share (1) 47 98 886 (1) Shares were excluded from the dilutive-effect calculation because the outstanding awards' exercise prices were greater than the average market price the Company's common stock (for 2018 and 2017) and Knight's common stock (for 2016).

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Carrying Amounts And Estimated Fair Values Of Financial Instruments	Financial Liabilities — The following table presents the carrying amounts and estimated fair values of the Company's financial instruments: December 31, 2018 2017 Carrying Estimated Carrying Estimated (In thousands) Term Loan, due October 2020 (1) $ 364,590 $ 365,000 $ 364,355 $ 365,000 2018 RSA, due July 2021 (2) 239,606 240,000 — — 2015 RSA, due January 2019 — — 305,000 305,000 Revolver, due October 2022 195,000 195,000 125,000 125,000 (1) The carrying amount of the Term Loan is included in "Long-term debt – less current portion," and is net of $0.4 million and $0.6 million in deferred loan costs as of December 31, 2018 and 2017 , respectively. (2) The carrying amount of the 2018 RSA is included in "Accounts receivable securitization," and is net of $0.4 million deferred loan costs as of December 31, 2018 .
Assets That Were Measured At Estimated Fair Value On Recurring 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 recurring basis as of December 31, 2018 and 2017 : Fair Value Measurements at Reporting Date Using Estimated Fair Value (1) Level 1 Inputs Level 2 Inputs Level 3 Inputs (In thousands) As of December 31, 2018 Money market funds $ 1,602 $ 1,602 $ — $ — Debt securities – municipal securities 2,524 — 2,524 — As of December 31, 2017 Money market funds 1,427 1,427 — — Debt securities – municipal securities 1,887 — 1,887 — (1) The money market funds and debt securities are trading securities and are restricted to meet statutory requirements. The carrying value, included within "Other long-term assets" in the Company's consolidated balance sheets, approximates the estimated fair value.
Assets That Were Measured At Estimated Fair Value On Non-Recurring Basis	The following table presents assets measured at estimated fair value on a nonrecurring basis as of December 31, 2018 and 2017 : Fair Value Measurements at Reporting Date Using Estimated Fair Value Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Losses (In thousands) As of December 31, 2018 Software (1) $ — $ — $ — $ — $ (550 ) Equipment (2) 2,800 — 2,800 — (2,248 ) As of December 31, 2017 Software (3) $ — $ — $ — $ — $ (16,746 ) Equipment (4) 350 — — 350 (98 ) (1) During the fourth quarter of 2018, the Company incurred impairment charges related to replaced software systems of $0.6 million . (2) During the fourth quarter of 2018, the Company incurred impairment charges related to the Company airplane of $2.2 million . This impairment was allocated between the Knight Trucking and Knight Logistics segments based on each segment’s use of the asset. (3) The Company terminated the implementation of Swift's ERP system in 2017. The related impairment loss was included in "Impairments" within operating income in the consolidated income statement (within Swift's non-reportable segments). (4) Management reassessed the fair value of certain Interstate Equipment Leasing, LLC tractors as of December 31, 2017 , which had a total book value of $0.4 million , determining that there was an impairment loss. The impairment loss was included in "Impairments" within operating income in the consolidated income statement (within Swift's non-reportable segments).

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2018
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: 2018 2017 2016 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) $ 681 $ — $ 161 $ — $ — $ — SME Industries (1) 698 — 275 — — — Total $ 1,379 $ — $ 436 $ — $ — $ — Facility and Equipment Leases: Central Freight Lines (1) $ 916 $ 370 $ 245 $ 92 $ — $ — Other Affiliates (1) 19 — — — — — Total $ 935 $ 370 $ 245 $ 92 $ — $ — Other Services: Updike Distribution Logistics, LLC (2) $ 554 $ — $ 2,771 $ — $ 1,433 $ — Other Affiliates (1) 35 2,590 48 604 — — Total $ 589 $ 2,590 $ 2,819 $ 604 $ 1,433 $ — (1) Entities affiliated with former Board member Jerry Moyes include Central Freight Lines, SME Industries, Compensi Services, and DPF Mobile. Transactions with these entities that are controlled by and/or are otherwise affiliated with Jerry Moyes, include freight services, facility leases, equipment sales, and other services. • Freight Services Provided by Knight-Swift — The Company charges for freight services to each of these companies for transportation services. • Freight Services Received by Knight-Swift — Transportation services received from Central Freight 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 and certain third-party payroll and employee benefits administration services from the identified related parties are included in other services received by the Company. • In conjunction with Swift's September 8, 2016 announcement that Jerry Moyes would retire from his position as Chief Executive Officer effective December 31, 2016, Swift entered into an agreement with Mr. Moyes to memorialize the terms of his retirement, which was assumed by Knight-Swift. Swift contracted with Mr. Moyes to serve as a non-employee consultant from January 1, 2017 through December 31, 2019 , during which time Swift will pay Mr. Moyes a monthly consulting fee in cash. The following is a rollforward of the accrued liability for the consulting fees: (In thousands) Accrued consulting fees – Jerry Moyes, balance at December 31, 2017 (1a) $ 4,450 Additions to accrual — Less: payments (2,225 ) Accrued consulting fees – Jerry Moyes, balance at December 31, 2018 (1a) $ 2,225 (1a) The balance is included in "Other long-term liabilities" (noncurrent) and "Accrued liabilities" (current) in the consolidated balance sheets, based on the timing of the expected payments. (2) Knight had an arrangement with Updike Distribution Logistics, LLC, a company that is owned by the father and three brothers of Executive Vice President of Sales and Marketing, James Updike, Jr. The arrangement allowed Updike Distribution Logistics, LLC to purchase fuel from Knight's vendors at cost, plus an administrative fee. The arrangement was terminated during the second quarter of 2018. Receivables and payables pertaining to related party transactions were: December 31, 2018 2017 Receivable Payable Receivable Payable (In thousands) Central Freight Lines $ 254 $ — $ 213 $ — SME Industries 24 — 79 — Other Affiliates — 20 — — Total $ 278 $ 20 $ 292 $ —
Jerry Moyes's consulting fees rollforward	The following is a rollforward of the accrued liability for the consulting fees: (In thousands) Accrued consulting fees – Jerry Moyes, balance at December 31, 2017 (1a) $ 4,450 Additions to accrual — Less: payments (2,225 ) Accrued consulting fees – Jerry Moyes, balance at December 31, 2018 (1a) $ 2,225 (1a) The balance is included in "Other long-term liabilities" (noncurrent) and "Accrued liabilities" (current) in the consolidated balance sheets, based on the timing of the expected payments.

Information by Segment, Geogr_2

Information by Segment, Geography, and Customer Concentration (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Summary Of Financial Information By Segments	The following tables present the Company's financial information by segment: 2018 2017 2016 Total revenue: (Dollars in thousands) Knight – Trucking $ 1,144,125 21.4 % $ 906,484 37.4 % $ 900,368 80.5 % Knight – Logistics $ 334,108 6.3 % $ 234,155 9.7 % $ 226,912 20.3 % Swift – Truckload $ 1,680,882 31.5 % $ 609,112 25.1 % $ — — % Swift – Dedicated $ 646,057 12.1 % $ 200,628 8.3 % $ — — % Swift – Refrigerated $ 819,190 15.3 % $ 254,102 10.5 % $ — — % Swift – Intermodal $ 470,165 8.8 % $ 130,441 5.4 % $ — — % Subtotal $ 5,094,527 95.4 % $ 2,334,922 96.4 % $ 1,127,280 100.8 % Non-reportable segments $ 314,732 5.8 % $ 115,530 4.8 % $ — — % Intersegment eliminations $ (65,193 ) (1.2 )% $ (24,999 ) (1.2 )% $ (9,246 ) (0.8 )% Total revenue $ 5,344,066 100.0 % $ 2,425,453 100.0 % $ 1,118,034 100.0 % 2018 2017 2016 Operating income (loss): (Dollars in thousands) Knight – Trucking $ 209,099 36.7 % $ 92,298 46.0 % $ 136,229 91.7 % Knight – Logistics $ 24,917 4.4 % $ 12,600 6.3 % $ 12,250 8.3 % Swift – Truckload $ 225,436 39.6 % $ 74,924 37.3 % $ — — % Swift – Dedicated $ 81,942 14.4 % $ 22,410 11.2 % $ — — % Swift – Refrigerated $ 34,341 6.0 % $ 13,626 6.8 % $ — — % Swift – Intermodal $ 30,127 5.3 % $ 5,977 3.0 % $ — — % Subtotal $ 605,862 106.4 % $ 221,835 110.6 % $ 148,479 100.0 % Non-reportable segments $ (36,819 ) (6.4 )% $ (21,205 ) (10.6 )% $ — — % Operating income $ 569,043 100.0 % $ 200,630 100.0 % $ 148,479 100.0 % 2018 2017 2016 Depreciation and amortization of property and equipment: (Dollars in thousands) Knight – Trucking $ 121,376 31.3 % $ 111,536 57.6 % $ 111,242 96.2 % Knight – Logistics $ 4,441 1.1 % $ 5,089 2.6 % $ 4,418 3.8 % Swift – Truckload $ 106,901 27.6 % $ 32,258 16.7 % $ — — % Swift – Dedicated $ 50,209 13.0 % $ 14,381 7.4 % $ — — % Swift – Refrigerated $ 40,724 10.5 % $ 11,163 5.8 % $ — — % Swift – Intermodal $ 11,951 3.1 % $ 3,231 1.7 % $ — — % Subtotal $ 335,602 86.6 % $ 177,658 91.8 % $ 115,660 100.0 % Non-reportable segments $ 51,903 13.4 % $ 16,075 8.2 % $ — — % Consolidated depreciation and amortization of property and equipment $ 387,505 100.0 % $ 193,733 100.0 % $ 115,660 100.0 %

Quarterly Result of Operation_2

Quarterly Result of Operations (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Information [Abstract]
Quarterly Results of Operations (Unaudited)	In management's opinion, the following summarized financial information fairly presents the Company's results of operations for the quarters noted. These results are not necessarily indicative of future quarterly results. First Quarter Second Quarter Third Quarter Fourth Quarter (In thousands, except per share data) 2018 Total revenue $ 1,271,132 $ 1,331,683 $ 1,346,611 $ 1,394,640 Net income 70,732 91,628 106,344 151,945 Net income attributable to Knight-Swift 70,364 91,323 105,881 151,696 Basic earnings per share 0.39 0.51 0.60 0.87 Diluted earnings per share 0.39 0.51 0.60 0.86 2017 Total revenue $ 271,182 $ 273,243 $ 521,608 $ 1,359,420 Net income 15,106 18,259 4,199 447,861 Net income attributable to Knight-Swift 14,876 17,970 3,881 447,564 Basic earnings per share 0.19 0.22 0.04 2.52 Diluted earnings per share 0.18 0.22 0.04 2.50

Introduction and Basis of Pre_3

Introduction and Basis of Presentation (Description of Business) (Details)	12 Months Ended
	Dec. 31, 2018SegmentVehicle
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number Of Company Operated National Terminal Network And Tractor Fleet	19,156
Number Of Tractors Driven By Company Drivers	15,743
Number Of Owner Operator Tractors	3,413
Number Of Fleet Of Trailers	69,544
Number Of Intermodal Tractors	640
Number Of Intermodal Containers	9,330
Number of Reportable Segments | Segment	6

Introduction and Basis of Pre_4

Introduction and Basis of Presentation Introduction and Basis of Presentation (2017 Merger) (Details)	Sep. 08, 2017
Knight Transportation Company [Member]
Business Acquisition [Line Items]
Ownership Percentage, Shares Outstanding	46.00%
Swift Transportation Company [Member]
Business Acquisition [Line Items]
Ownership Percentage, Shares Outstanding	54.00%

Introduction and Basis of Pre_5

Introduction and Basis of Presentation Introduction and Basis of Presentation (Basis of Presentation) (Details)	12 Months Ended
	Dec. 31, 2018
Kold Trans, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Joint Venture Ownership Interest	80.00%
Commercial vehicle parts, joint venture [Member]
Schedule of Equity Method Investments [Line Items]
Joint Venture Ownership Interest	52.00%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2018
Percentage Of Income Tax Positions Likely To Be Realized	50.00%
Customer Relationships [Member] | Minimum [Member]
Finite-Lived Intangible Asset, Useful Life	5 years
Customer Relationships [Member] | Maximum [Member]
Finite-Lived Intangible Asset, Useful Life	20 years
Revenue Equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	4 years
Revenue Equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	20 years
Shop and service equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	2 years
Shop and service equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	10 years
Land Improvements [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	5 years
Land Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	15 years
Building and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	10 years
Building and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	40 years
Furniture and Fixtures [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	3 years
Furniture and Fixtures [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	10 years

Recently Adopted Accounting P_4

Recently Adopted Accounting Pronouncements Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Trade receivables, net of allowance for doubtful accounts of $16,355 and $14,829, respectively	$ 616,830				$ 574,265				$ 616,830	$ 574,265		$ 16,992
Accrued payroll and purchased transportation	126,464				107,017				126,464	107,017
Accrued liabilities	151,500				186,379				151,500	186,379
Deferred Income Tax Liabilities, Net	739,538								739,538
Retained earnings	1,216,852				1,016,738				1,216,852	1,016,738
Total revenue	1,394,640	$ 1,346,611	$ 1,331,683	$ 1,271,132	1,359,420	$ 521,608	$ 273,243	$ 271,182	5,344,066	2,425,453	$ 1,118,034
Salaries, wages, and benefits									1,495,126	688,543	333,929
Operations and maintenance									340,627	164,307	76,246
Purchased transportation									1,318,303	594,113	233,863
Operating Expenses									4,775,023	2,224,823	969,555
Income tax expense (benefit)									131,389	(291,716)	57,592
Net income Attributable to Knight-Swift	151,696	$ 105,881	$ 91,323	$ 70,364	447,564	$ 3,881	$ 17,970	$ 14,876	419,264	484,292	93,863
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Trade receivables, net of allowance for doubtful accounts of $16,355 and $14,829, respectively	601,228				574,265				601,228	574,265
Accrued payroll and purchased transportation	117,341				107,017				117,341	107,017
Accrued liabilities	152,506				186,076				152,506	186,076
Deferred Income Tax Liabilities, Net	736,803				679,077				736,803	679,077
Retained earnings	1,212,102				1,016,738				1,212,102	1,016,738
Salaries, wages, and benefits									1,495,480
Operations and maintenance									340,645
Purchased transportation									1,318,546
Income tax expense (benefit)									131,613
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Trade receivables, net of allowance for doubtful accounts of $16,355 and $14,829, respectively												$ 17,000
Accrued payroll and purchased transportation	9,123				9,720				9,123	9,720
Accrued liabilities					201					201
Increase (Decrease) in Accrued Liabilities									(1,006)
Deferred Income Tax Liabilities, Net	2,735				1,770				2,735	1,770
Retained earnings	$ 4,750				5,301				4,750	5,301
Total revenue									(1,390)
Salaries, wages, and benefits									354
Operations and maintenance									18
Purchased transportation									243
Operating Expenses									615
Income tax expense (benefit)									224
Net income Attributable to Knight-Swift									(551)
Adjusted Opening Balance [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Trade receivables, net of allowance for doubtful accounts of $16,355 and $14,829, respectively					591,257					591,257
Accrued payroll and purchased transportation					116,737					116,737
Accrued liabilities					186,277					186,277
Deferred Income Tax Liabilities, Net					680,847					680,847
Retained earnings					$ 1,022,039					1,022,039
Revenue, excluding fuel surcharge [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue									4,725,288	2,179,873	1,028,148
Revenue, excluding fuel surcharge [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue									4,726,578
Revenue, excluding fuel surcharge [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue									(1,290)
Fuel surcharge revenue [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue									618,778	$ 245,580	$ 89,886
Fuel surcharge revenue [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue									618,878
Fuel surcharge revenue [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue									$ (100)

Recently Adopted Accounting P_5

Recently Adopted Accounting Pronouncements Cash Flow Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 82,486	$ 76,649		$ 8,021
Other Noncash Income (Expense)	4,617	14,758	[1]	802
Net Cash Provided by (Used in) Operating Activities	881,977	322,590		243,776
Increase (Decrease) in Restricted Cash		0		0
Net cash, restricted cash, and equivalents (invested in) acquired from merger and acquisitions	(101,693)	91,960		0
Other cash flows from investing activities	10,085	9,953	[1]	(12,059)	[2]
Net Cash Provided by (Used in) Investing Activities	(647,292)	(204,263)		(101,060)
Net (decrease) increase in cash, restricted cash, and equivalents	(20,757)	142,327		(288)
Cash, restricted cash, and equivalents at beginning of period	130,976	151,733		9,406		$ 9,694
Cash and cash equivalents — restricted	46,888	73,657		0
Restricted Cash and Cash Equivalents, Noncurrent	$ 1,602	1,427		1,385
Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other Noncash Income (Expense)		10,737	[1]	380
Net Cash Provided by (Used in) Operating Activities		318,569		243,354
Increase (Decrease) in Restricted Cash		(10,215)		(6)
Net cash, restricted cash, and equivalents (invested in) acquired from merger and acquisitions		28,493
Other cash flows from investing activities		13,957	[1]	(12,013)	[2]
Net Cash Provided by (Used in) Investing Activities		(273,941)		(101,020)
Net (decrease) increase in cash, restricted cash, and equivalents		68,628		(670)
Cash, restricted cash, and equivalents at beginning of period		76,649		8,021		8,691
Accounting Standards Update 2016-05 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other Noncash Income (Expense)		4,021	[1]	422
Net Cash Provided by (Used in) Operating Activities		4,021		422
Increase (Decrease) in Restricted Cash		0		0
Net cash, restricted cash, and equivalents (invested in) acquired from merger and acquisitions		0
Other cash flows from investing activities		(4,021)	[1]	(422)	[2]
Net Cash Provided by (Used in) Investing Activities		(4,021)		(422)
Net (decrease) increase in cash, restricted cash, and equivalents		0		0
Cash, restricted cash, and equivalents at beginning of period		0		0		0
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other Noncash Income (Expense)		0	[1]	0
Net Cash Provided by (Used in) Operating Activities		0		0
Increase (Decrease) in Restricted Cash		10,215		6
Net cash, restricted cash, and equivalents (invested in) acquired from merger and acquisitions		63,467
Other cash flows from investing activities		17	[1]	376	[2]
Net Cash Provided by (Used in) Investing Activities		73,699		382
Net (decrease) increase in cash, restricted cash, and equivalents		73,699		382
Cash, restricted cash, and equivalents at beginning of period		$ 75,084		$ 1,385		$ 1,003
[1]	See Note 1 for line items that were previously separately presented, but are included in "Other adjustments to reconcile net income to net cash provided by operating activities" and "Other cash flows from investing activities" for the current period presentation.
[2]	See footnote (1) in table above.

Recently Adopted Accounting P_6

Recently Adopted Accounting Pronouncements Impact of SAB 118 (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Transition tax		$ 300	$ 3,200
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		452	(367,000)	$ 0
Income tax expense (benefit)		131,389	$ (291,716)	$ 57,592
Tax Cuts and Jobs Act Benefit [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		367,000
Temporary differences [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Cuts and Jobs Act temporary difference		2,900
Income tax expense (benefit)		400
Legal reserve adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable and Accrued Liabilities	[1]	(6,500)
Income tax expense (benefit)		$ 900
[1]	Adjustments made to accrued liabilities, goodwill, and deferred tax liabilities due to new information obtained related to certain legal matters that were outstanding as of the 2017 Merger closing date.

Recently Issued Accounting Pr_3

Recently Issued Accounting Pronouncements (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Accounting Standards Update 2018-20 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The amendments in this ASU provide entities with additional guidance about the recognition of variable payments for contracts with lease and nonlease components. These amendments provide lessors the option to exclude certain lessor costs from recognition. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted.
Expected Adoption Date and Method	Refer to ASU 2016-02, below
Financial Statement Impact	Refer to ASU 2016-02, below
Accounting Standards Update 2018-19 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The amendments in this ASU make targeted improvements to the implementation guidance in ASU 2016-13. The amendments clarify that receivables arising from operating leases are not within the scope of ASC 326-20, but instead should be accounted for in accordance with Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted.
Expected Adoption Date and Method	January 2020, Modified retrospective
Financial Statement Impact	Currently under evaluation, but not expected to be material
Accounting Standards Update 2018-15 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The amendments align the requirements for capitalizing implementation costs in a hosting arrangement with the guidance for internal-use software, resulting in expensing preliminary or post-implementation project costs and capitalizing certain application development costs. The capitalized costs should be included in the balance sheet line that includes prepayment for the fees of the associated hosting arrangement, and amortized over the noncancellable period of the arrangement. Amortization expense should be included in the income statement line that includes the fees associated with the hosting element of the arrangement. Payments for capitalized implementation costs should be classified in the statement of cash flows in the same manner as payments made for hosting element fees. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted.
Expected Adoption Date and Method	January 2020, Prospective
Financial Statement Impact	Currently under evaluation, but not expected to be material
Accounting Standards Update 2018-13 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The amendments in this ASU modify several disclosure requirements under Topic 820. These changes include removing the disclosure requirements related to the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, and adding disclosure requirements about the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Additionally, the amendments remove the phrase "at a minimum" from the codification clarifying that materiality should be considered when evaluating disclosure requirements. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019. Early adoption is permitted.
Expected Adoption Date and Method	January 2019, Retrospective
Financial Statement Impact	Not expected to be material (1)	[1]
Accounting Standards Update 2018-11 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The amendments in this ASU provide entities with an additional transition method for implementing ASC Topic 842, in which entities have the option to apply the new standard at the adoption date, recognizing a cumulative-effect adjustment to the opening balance of retained earnings. Comparative periods would not be restated, and would instead be presented under the legacy ASC Topic 840 guidance. Under certain conditions, the amendments in this ASU also provide lessors a practical expedient regarding separating nonlease components from the associated lease components if the nonlease components would otherwise be accounted for under ASC Topic 606, Revenue from Contracts with Customers. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted.
Expected Adoption Date and Method	Refer to ASU 2016-02, below
Financial Statement Impact	Refer to ASU 2016-02, below
Accounting Standards Update 2018-10 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	This ASU contains various amendments to ASC Topic 842 that clarify the language, remove inconsistencies, and improve upon other issues, including those associated with implementing the new standard. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted.
Expected Adoption Date and Method	Refer to ASU 2016-02, below
Financial Statement Impact	Refer to ASU 2016-02, below
Accounting Standards Update 2018-07 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The amendments in this ASU expand the scope of ASC Topic 718 to include share-based payments to nonemployees, and for public business entities include 1) measuring awards to nonemployees at grant-date fair value, 2) measuring awards to nonemployees at the grant date, 3) for awards with performance conditions granted to nonemployees, assessing the probability of satisfying performance conditions when measuring such awards, and 4) generally subjecting equity-classified awards to the requirements of ASC Topic 718, eliminating the requirement to reassess classification upon vesting. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted.
Expected Adoption Date and Method	January 2019, Modified retrospective
Financial Statement Impact	Currently under evaluation (2)	[2]
Accounting Standards Update 2018-01 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The amendments in this ASU permit entities to elect to exclude land easements which were not previously recorded as leases from the evaluation related to the adoption of ASC Topic 842. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted.
Expected Adoption Date and Method	Refer to ASU 2016-02, below
Financial Statement Impact	Refer to ASU 2016-02, below
Accounting Standards Update 2017-04 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The amendments in this ASU are intended to simplify subsequent measurement of goodwill. The key amendment in the ASU eliminates Step 2 from the goodwill impairment test, in which entities measured a goodwill impairment loss by comparing the implied fair value to the carrying amount of a reporting unit's goodwill. Instead, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value with the carrying amount of a reporting unit and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value.
Expected Adoption Date and Method	January 2020, prospective
Financial Statement Impact	Currently under evaluation; not expected to be material
Accounting Standards Update 2016-13 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The purpose of this ASU is to amend the current incurred loss impairment methodology with a new methodology that reflects expected credit losses and requires a broader range of reasonable and supportable information to inform credit loss estimates. This is the final credit accounting standard, out of a series, with detailed guidance on the new loss reserve model, Current Expected Credit Loss ("CECL"). Among other provisions, the amendments in the ASU require a financial asset (or group of assets) measured at amortized cost basis to be presented at the net amount expected to be collected. Entities are no longer required to wait until a loss is probable to record it.
Expected Adoption Date and Method	January 2020, Adoption method varies by amendment
Financial Statement Impact	Currently under evaluation; not expected to be material
Accounting Standards Update 2016-02 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Description	The new standard requires lessees to recognize assets and liabilities arising from both operating and financing leases on the balance sheet. Lessor accounting for leases is largely unaffected. For public business entities, the new standard is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted.
Expected Adoption Date and Method	January 2019, Modified retrospective - cumulative-effect adjustment to beginning balance of retained earnings at the adoption date
Financial Statement Impact	Expected to be material (3)	[3]
Minimum [Member]
Recently Issued Accounting Pronouncements [Line Items]
Operating Lease, Right-of-Use Asset	$ 270
Operating Lease, Liability	270
Maximum [Member]
Recently Issued Accounting Pronouncements [Line Items]
Operating Lease, Right-of-Use Asset	300
Operating Lease, Liability	$ 300
[1]	ASU 2018-13: Fair Value Measurement (Topic 820): Disclosure Framework – Change to the Disclosure Requirements for Fair Value Measurement — Upon adoption, management expects to have fewer disclosures regarding its fair value measurements as a result of the amendments that eliminate "at a minimum" from the phrase, "an entity shall disclose at a minimum." The amendments are intended to allow entities to exercise discretion when considering fair value disclosures, including materiality considerations. Accordingly, the Company will exclude immaterial disclosures regarding fair value measurements from its quarterly and annual reports upon adoption, beginning in the first quarter of 2019.
[2]	ASU 2018-07: Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting — In accordance with the amendments in this ASU, the Company will be required to measure any nonemployee liability-classified awards that have not been settled by the adoption date and any equity-classified awards for which a measurement date has not been established through a cumulative-effect adjustment to retained earnings as of January 1, 2019. The Company is not expecting a material impact from adopting the amendments in this ASU, as the Company will have no unvested share-based payment awards related to its nonemployee directors as of January 1, 2019.
[3]	ASC 842, Leases — The Company established an implementation team, which includes support from external experts, to transition the Company from accounting for leases under ASC 840 to accounting for leases under ASC 842. The diagnostic phase of implementing the new standard is complete, and management has selected practical expedients and accounting policies to evaluate the lease population. The Company is substantially complete with the process of extracting and uploading lease data available from existing systems and documents into its new lease software solution. Management expects to elect the package of practical expedients (regarding lease identification, lease classification, and initial direct costs), but not the hindsight practical expedient. Additionally, management expects to elect accounting policies to account for its revenue equipment leases at the portfolio level, to bundle nonlease components with their related lease components (as lessee), and to not recognize a right-of-use asset or lease liability for short-term leases. These policies are not substantially different from the Company’s current accounting policies.After considering the above practical expedient and accounting policy elections, management expects that adopting the new lease standard will result in adding right-of-use assets of $270.0 million to $300.0 million and corresponding lease liabilities of $270.0 million to $300.0 million to the consolidated balance sheet as of January 1, 2019, with the net impact being recorded as a cumulative-effect adjustment to retained earnings, as applicable. The impact of adopting the new lease standard is not expected to be material to the Company’s consolidated income statement, liquidity, or compliance with debt covenants.

Merger and Acquisition (2017 Me

Merger and Acquisition (2017 Merger - fair value consideration transferred) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Sep. 08, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 09, 2017	Dec. 31, 2015
Business Acquisition [Line Items]
Net income Attributable to Knight-Swift		$ 151,696	$ 105,881	$ 91,323	$ 70,364	$ 447,564	$ 3,881	$ 17,970	$ 14,876		$ 419,264	$ 484,292	$ 93,863
Conversion Of Stock, Number Of Shares Issued Per Share Converted	$ 0.72
Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Shares, Outstanding	134,765													97,031
Conversion Of Stock, Number Of Shares Issued Per Share Converted	$ 0.72
Fair value of the consideration transferred	$ 3,976,905									$ 0	$ 3,976,905
Knight Transportation Company [Member]
Business Acquisition [Line Items]
Ownership Percentage, Shares Outstanding	46.00%
Knight Transportation Company [Member] | Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price	$ 40.85
Swift Transportation Company [Member]
Business Acquisition [Line Items]
Net income Attributable to Knight-Swift												$ 95,700
Ownership Percentage, Shares Outstanding	54.00%
Common Stock [Member]
Business Acquisition [Line Items]
Shares, Outstanding		172,844				177,998				177,998	172,844	177,998	80,229		80,967
Common Stock [Member] | Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	$ 3,963,712
Equity Awards [Member] | Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	$ 13,193

Merger and Acquisition Merger_3

Merger and Acquisition Merger and Acquisition (2017 Merger - allocation of purchase consideration) (Details) - USD ($) $ in Thousands		Sep. 08, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 30, 2017
Business Acquisition [Line Items]
Goodwill	[1]		$ 2,887,867	$ 2,919,176
Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred		$ 3,976,905	$ 0	3,976,905
Cash		28,484		28,484	$ 0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Restricted Cash and Fixed Maturity Securities		85,615		85,615	0
Trade receivables		411,767		411,767	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense		44,564		44,564	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other		19,736		19,736	0
Property and equipment		1,522,123		1,522,123	0
Intangible assets	[2]	1,285,900		1,451,700	165,800	[3]
Other assets		18,537		18,537	0
Total assets		3,416,726		3,582,526	165,800
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable		(188,411)		(188,411)	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable and Accrued Liabilities	[4]	(232,280)		(238,746)	(6,466)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Claims Accruals		(306,846)		(306,846)	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt		(894,681)		(894,681)	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities	[2],[4]	(741,405)		(803,305)	(61,900)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other		(18,452)		(18,452)	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		(2,382,075)		(2,450,441)	(68,366)
Goodwill	[2],[4]	$ 2,942,254		$ 2,844,820	$ (97,434)
[1]	Except for the net accumulated amortization related to deferred tax assets in the Knight Trucking segment, the net carrying amount and gross carrying amount are equal since there are no accumulated impairment losses.
[2]	Adjustments made to identifiable intangible assets, goodwill, and deferred tax liabilities pertain to management's re-evaluation of the royalty rate used associated with certain trade names.
[3]	See (1), above for nature of the adjustments made to intangible assets.
[4]	Adjustments made to accrued liabilities, goodwill, and deferred tax liabilities due to new information obtained related to certain legal matters that were outstanding as of the 2017 Merger closing date.

Merger and Acquisition (2017 _2

Merger and Acquisition (2017 Merger intangible assets) (Details) - Knight-Swift Merger [Member] - USD ($) $ in Thousands		Sep. 08, 2017	Dec. 31, 2017	[1]	Dec. 31, 2018	Dec. 30, 2017	[1]
Acquired Finite-Lived Intangible Assets [Line Items]
Customer relationships		$ 817,200	$ 700		$ 816,500
Trade name		468,700	$ 166,500		635,200
Intangible assets	[2]	$ 1,285,900			$ 1,451,700	$ 165,800
Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		10 years
Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		20 years
[1]	See (1), above for nature of the adjustments made to intangible assets.
[2]	Adjustments made to identifiable intangible assets, goodwill, and deferred tax liabilities pertain to management's re-evaluation of the royalty rate used associated with certain trade names.

Merger and Acquisition - Narrat

Merger and Acquisition - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 08, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Total revenue		$ 1,394,640	$ 1,346,611	$ 1,331,683	$ 1,271,132	$ 1,359,420	$ 521,608	$ 273,243	$ 271,182		$ 5,344,066	$ 2,425,453	$ 1,118,034
Net income Attributable to Knight-Swift		$ 151,696	$ 105,881	$ 91,323	$ 70,364	$ 447,564	$ 3,881	$ 17,970	$ 14,876		419,264	484,292	93,863
Net Income											420,649	485,425	95,238
Merger-related costs											0	16,516	0
Salaries, wages, and benefits											1,495,126	688,543	333,929
Miscellaneous operating expenses											61,626	41,781	17,274
Purchased transportation											1,318,303	594,113	233,863
Amortization of Intangible Assets											42,584	13,372	$ 500
Conversion Of Stock, Number Of Shares Issued Per Share Converted	$ 0.72
Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred	$ 3,976,905									$ 0	3,976,905
Merger-related costs											16,500
Salaries, wages, and benefits											5,600
Miscellaneous operating expenses											900
Purchased transportation											$ 100
Amortization of Intangible Assets												12,900
Conversion Of Stock, Number Of Shares Issued Per Share Converted	$ 0.72
Knight Transportation Company [Member]
Business Acquisition [Line Items]
Ownership Percentage, Shares Outstanding	46.00%
Knight Transportation Company [Member] | Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price	$ 40.85
Swift Transportation Company [Member]
Business Acquisition [Line Items]
Total revenue												1,300,000
Net income Attributable to Knight-Swift												95,700
Ownership Percentage, Shares Outstanding	54.00%
Equity Awards [Member] | Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	$ 13,193
Acquisition-related Costs [Member] | Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Net Income												$ (57,000)

Merger and Acquisition (Abilene

Merger and Acquisition (Abilene Acquisition) (Details) - USD ($) $ in Thousands	Mar. 16, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Percentage of acquired business revenue		1.60%
Percentage of acquired business net income		2.10%
Percentage of acquired business assets		1.70%
Abilene [Member]
Business Acquisition [Line Items]
Percentage of equity interests acquired	100.00%
Fair value of the consideration transferred	$ 103,347	$ 103,300
Consideration for Equity Interests [Member] | Abilene [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred	80,500
Consideration for Debt Payments [Member] | Abilene [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred	22,800
Escrow For Sellers Indemnification Obligations [Member] | Abilene [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred	7,000
Escrow For Tax Obligations [Member] | Abilene [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred	4,500
Acquisition-related Costs [Member] | Abilene [Member]
Business Acquisition [Line Items]
Abilene Acquisition, transaction costs	$ 200

Merger and Acquisition (Abile_2

Merger and Acquisition (Abilene Acquisition Allocation of Purchase Consideration) (Details) - USD ($) $ in Thousands		Mar. 16, 2018	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	[1]		$ 2,919,176	$ 2,887,867
Abilene [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred		$ 103,347	$ 103,300
Cash		1,654
Trade receivables		13,010
Other assets		8,627
Property and equipment		41,403
Intangible assets	[2]	22,600
Total assets		87,294
Accounts payable		3,536
Accrued liabilities		7,361
Claims accruals		402
Total liabilities		11,299
Goodwill		27,352
Customer Relationship		17,900
Trade name		4,700
Previously Reported [Member] | Abilene [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred		103,223
Cash		1,654
Trade receivables		11,745
Other assets		7,785
Property and equipment		41,403
Intangible assets	[2]	23,000
Total assets		85,587
Accounts payable		1,959
Accrued liabilities		2,419
Claims accruals		230
Total liabilities		4,608
Goodwill		22,244
Restatement Adjustment [Member] | Abilene [Member]
Business Acquisition [Line Items]
Fair value of the consideration transferred		124
Cash		0
Trade receivables		1,265
Other assets		842
Property and equipment		0
Intangible assets	[2]	(400)
Total assets		1,707
Accounts payable		1,577
Accrued liabilities		4,942
Claims accruals		172
Total liabilities		6,691
Goodwill		$ 5,108
[1]	Except for the net accumulated amortization related to deferred tax assets in the Knight Trucking segment, the net carrying amount and gross carrying amount are equal since there are no accumulated impairment losses.
[2]	Includes a $17.9 million customer relationship and a $4.7 million trade name.

Merger and Acquisition (2017 _3

Merger and Acquisition (2017 Merger Pro-forma information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Salaries, wages, and benefits									$ 1,495,126	$ 688,543	$ 333,929
Amortization of Intangible Assets									42,584	13,372	500
Total revenue	$ 1,394,640	$ 1,346,611	$ 1,331,683	$ 1,271,132	$ 1,359,420	$ 521,608	$ 273,243	$ 271,182	5,344,066	2,425,453	1,118,034
Net income Attributable to Knight-Swift	$ 151,696	$ 105,881	$ 91,323	$ 70,364	$ 447,564	$ 3,881	$ 17,970	$ 14,876	419,264	484,292	$ 93,863
Total revenue									5,366,551	5,230,674
Net Income Attributable to Knight-Swift									$ 419,812	$ 536,062
Diluted earnings per share									$ 2.36	$ 3
Knight-Swift Merger [Member]
Business Acquisition [Line Items]
Salaries, wages, and benefits									$ 5,600
Amortization of Intangible Assets										$ 12,900
Swift Transportation Company [Member]
Business Acquisition [Line Items]
Total revenue										1,300,000
Net income Attributable to Knight-Swift										95,700
Fair Value, Measurements, Nonrecurring [Member]
Business Acquisition [Line Items]
Impairment of Intangible Assets, Finite-lived										$ 16,800

Marketable Securities Marketa_3

Marketable Securities Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Marketable Securities [Abstract]
Sale Proceeds	$ 0	$ 0	$ 7,403
Cost of securities sold	0	0	2,909
Gross Realized Gains	0	0	4,494
Realized gain, net of taxes	0	0	$ 2,771
Available-for-sale Securities, Equity Securities	$ 0	$ 0

Restricted Investments, Held-_3

Restricted Investments, Held-to-Maturity (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)Securities	Dec. 31, 2017USD ($)Securities
Schedule of Restricted Investments [Line Items]
Cost or Amortized Cost	$ 17,413	$ 22,232
Gross Unrealized, Gains	1	0
Gross Unrealized, Temporary Losses	(16)	(24)
Estimated Fair Value	$ 17,398	$ 22,208
Restricted held to maturity investments	1 year
Securities with unrealized losses for less than 12 months | Securities	20	32
Duration of securities in unrealized loss position	12 months
United States corporate securities
Schedule of Restricted Investments [Line Items]
Cost or Amortized Cost	$ 15,296	$ 15,982
Gross Unrealized, Gains	1	0
Gross Unrealized, Temporary Losses	(16)	(14)
Estimated Fair Value	15,281	15,968
Municipal bonds
Schedule of Restricted Investments [Line Items]
Cost or Amortized Cost	1,082	4,970
Gross Unrealized, Gains	0	0
Gross Unrealized, Temporary Losses	0	(10)
Estimated Fair Value	1,082	4,960
Negotiable certificate of deposits
Schedule of Restricted Investments [Line Items]
Cost or Amortized Cost	1,035	1,280
Gross Unrealized, Gains	0	0
Gross Unrealized, Temporary Losses	0	0
Estimated Fair Value	$ 1,035	$ 1,280

Transportation Resource Partn_3

Transportation Resource Partners Transportation Resource Partners (Investments and commitments) (Details) $ in Thousands	Dec. 31, 2018USD ($)
Transportation Resource Partners [Member]
Schedule of Equity Method Investments [Line Items]
TRP ownership interest	2.30%	[1],[2]
Total TRP investment commitment	$ 260,000
Amounts Committed To Invest	5,500
Remaining Investment Commitment	$ 0
Transportation Resource Partners III [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	5.30%	[2],[3]
Total TRP investment commitment	$ 245,000
Amounts Committed To Invest	15,000
Remaining Investment Commitment	1,715
TRP Investment Commitment, Due in Second and Third Year	$ 1,700
Transportation Resource Partners IV [Member]
Schedule of Equity Method Investments [Line Items]
TRP ownership interest	4.10%	[1],[2],[4]
Total TRP investment commitment	$ 116,000
Amounts Committed To Invest	4,900
Remaining Investment Commitment	2,002
TRP Investment Commitment, Due in Next Twelve Months	1,000
TRP Investment Commitment, Due in Second and Third Year	200
TRP Investment Commitment, Due in Fourth and Fifth Year	200
TRP Investment Commitment, Due after Fifth Year	$ 600
Transportation Resource Partners, Colnvest Partners, (NTI) [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	8.30%	[2],[5]
Total TRP investment commitment	$ 120,000
Amounts Committed To Invest	10,000
Remaining Investment Commitment	$ 0
Transportation Resource Partners, CoInvest Partners, (QLS) [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	25.00%	[2],[5]
Total TRP investment commitment	$ 39,000
Amounts Committed To Invest	9,735
Remaining Investment Commitment	$ 0
[1]	In accordance with ASC 321, Investments – Equity Securities, these investments are recorded at cost minus impairment.
[2]	Knight's share of the results is included within "Other income, net" in the consolidated income statements.
[3]	Management anticipates that the following amounts will be due: $1.7 million from 2020 through 2021.
[4]	Management anticipates that the following amounts will be due: $1.0 million in 2019, $0.2 million from 2020 through 2021, $0.2 million from 2022 through 2023, and $0.6 million from 2024 through 202
[5]	The TRP Coinvestments are unconsolidated majority interests. Management considered the criteria set forth in ASC 323, Investments – Equity Method and Joint Ventures, to establish the appropriate accounting treatment for these investments. This guidance requires the use of the equity method for recording investments in limited partnerships where the "so minor" interest is not met. As such, the investments are being accounted for under the equity method. Knight's ownership interest reflects its ultimate ownership of the portfolio companies underlying the TRP Coinvestment NTI and TRP Coinvestment QLS legal entities.

Transportation Resource Partn_4

Transportation Resource Partners Transportation Resource Partners (Carrying Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2018		Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	$ 20,646		$ 20,394
Transportation Resource Partners [Member]
Schedule of Equity Method Investments [Line Items]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	211	[1]	211
Transportation Resource Partners III [Member]
Schedule of Equity Method Investments [Line Items]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	1,781		1,973
Transportation Resource Partners IV [Member]
Schedule of Equity Method Investments [Line Items]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	2,022	[1]	2,577
Transportation Resource Partners, Colnvest Partners, (NTI) [Member]
Schedule of Equity Method Investments [Line Items]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	5,547		7,579
Transportation Resource Partners, CoInvest Partners, (QLS) [Member]
Schedule of Equity Method Investments [Line Items]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	$ 11,085		$ 8,054
[1]	In accordance with ASC 321, Investments – Equity Securities, these investments are recorded at cost minus impairment.

Transportation Resource Partn_5

Transportation Resource Partners - Subsequent event (Details) $ in Millions	Jan. 01, 2019USD ($)
Subsequent Event Type [Domain]
Subsequent Event [Line Items]
Amounts Committed To Invest	$ 4.9

Trade Receivables, net (Schedul

Trade Receivables, net (Schedule Of Trade Receivables) (Details) - USD ($) $ in Thousands	Dec. 31, 2018		Dec. 31, 2017
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Accounts receivable, gross	$ 633,185		$ 589,094
Less: Allowance for doubtful accounts	(16,355)		(14,829)
Trade receivables, net (1)	616,830	[1]	574,265
Contract with Customer, Asset, Net	15,602
Trade Customers [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Accounts receivable, gross	597,077		565,732
Equipment Manufacturers [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Accounts receivable, gross	7,166		6,017
Other [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Accounts receivable, gross	$ 28,942		$ 17,345
[1]	Includes $15.6 million of in-transit revenue as of December 31, 2018.

Trade Receivables, net Trade Re

Trade Receivables, net Trade Receivables, net (Rollforward of the allowance for doubtful accounts for trade receivables) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	$ 14,829
Ending balance	16,355		$ 14,829
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	14,829		2,727		$ 3,106
(Reduction) provision	(3,092)		4,671		909
Write-offs directly against the reserve	(1,362)		(1,583)		0
Write-offs for revenue adjustments	5,861		(3,758)		(1,288)
Other	119	[1]	12,772	[1]	0
Ending balance	$ 16,355		$ 14,829		$ 2,727
[1]	Increase in allowance for doubtful accounts relates to trade receivables assumed in 2017 from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions.

Notes Receivable, net (Schedule

Notes Receivable, net (Schedule of Notes Receivable) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross notes receivable	$ 16,393	$ 16,842
Allowance for doubtful notes receivable	(1,051)	(1,040)
Total notes receivable, net of allowance	15,342	15,802
Current portion, net of allowance	4,563	4,742
Long-term portion	10,779	11,060
Independent Contractor Relationship [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross notes receivable	9,318	8,977
Other Relationship [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross notes receivable	$ 7,075	$ 7,865
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable interest rate	2.00%
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable interest rate	20.00%

Notes Receivable, net Notes Rec

Notes Receivable, net Notes Receivable, net (Scheduled of Allowance for Doubtful Accounts) (Details) - SEC Schedule, 12-09, Allowance, Notes Receivable [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 1,040		$ 240		$ 273
Provision for doubtful accounts and notes receivables	(100)		574		(27)
Write-offs directly against the reserve	(103)		(53)		(6)
Other	214	[1]	279	[1]	0
Ending Balance	$ 1,051		$ 1,040		$ 240
[1]	Increase in allowance for doubtful notes relates to notes receivable in 2017 assumed from Swift as part of the 2017 Merger and in 2018 from the Abilene Acquisition. See Note 5 for further details regarding these transactions.

Assets Held for Sale (Narrative

Assets Held for Sale (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long Lived Assets Held-for-sale [Line Items]
Period of time assets are expected to be sold, months	12 months
Assets held for sale	$ 39,955	$ 25,153
Gain on sale of property and equipment	36,236	8,939	$ 8,124
Impairments	2,798	16,844	0
Land And Facilities [Member]
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale	0	0
Revenue Equipment [Member]
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale	40,000	25,200
Gain on sale of property and equipment	37,000	8,900
Impairments	$ 0	$ 0	$ 0

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets Schedule of Goodwill (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill at beginning of period		$ 2,887,867		$ 47,031
Amortization		(17)		(10)
Goodwill, Purchase Accounting Adjustments	[1]	3,974
Goodwill at end of period		2,919,176		2,887,867	$ 47,031
Net Carrying Amount	[2]	2,919,176		2,887,867
Goodwill, Impairment Loss		0		0	$ 0
Swift Truckload Goodwill
Goodwill [Line Items]
Goodwill, Purchase Accounting Adjustments		4,800
Net Carrying Amount	[2]	1,154,783		1,150,012
Swift Dedicated Goodwill
Goodwill [Line Items]
Goodwill, Purchase Accounting Adjustments		1,100
Net Carrying Amount	[2]	780,392		779,335
Swift Refrigerated Goodwill
Goodwill [Line Items]
Goodwill, Purchase Accounting Adjustments		(1,900)
Net Carrying Amount	[2]	648,759		650,613
Swift Intermodal Goodwill
Goodwill [Line Items]
Net Carrying Amount	[2]	175,594		175,594
Swift Non-Reportable Goodwill
Goodwill [Line Items]
Net Carrying Amount	[2]	85,292		85,292
Knight Trucking Goodwill
Goodwill [Line Items]
Net Carrying Amount	[2]	74,356		47,021
Abilene [Member]
Goodwill [Line Items]
Goodwill, Acquired During Period		$ 27,352	[3]	0
Knight-Swift Merger [Member]
Goodwill [Line Items]
Goodwill, Acquired During Period				$ 2,840,846
[1]	The goodwill adjustment associated with the 2017 Merger resulted in a $4.8 million increase, a $1.1 million increase, and a $1.9 million decrease in goodwill allocated to the Swift Truckload, Swift Dedicated, and Swift Refrigerated segments, respectively. See Note 5 regarding the nature of the adjustment.
[2]	Except for the net accumulated amortization related to deferred tax assets in the Knight Trucking segment, the net carrying amount and gross carrying amount are equal since there are no accumulated impairment losses.
[3]	The goodwill associated with the Abilene Acquisition was allocated to the Knight Trucking segment. See Note 5 regarding the amount attributed to adjustments to the March 17, 2018 opening balance sheet.

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets Schedule of Intangible Assets, net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Customer Relationships:
Gross carrying value	$ 838,100	$ 820,200
Accumulated amortization	(57,081)	(14,497)
Customer relationships, net	781,019	805,703
Trade Name:
Gross carrying value	639,900	635,200
Intangible assets, net	$ 1,420,919	$ 1,440,903

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets Finite-lived Intangible Assets Amortization Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Finite-Lived Intangible Assets Amortization Expense [Line Items]
Amortization of Intangible Assets	$ 42,584	$ 13,372	$ 500
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	42,700
Finite-Lived Intangible Assets, Amortization Expense, Year Two	42,600
Finite-Lived Intangible Assets, Amortization Expense, Year Three	42,700
Finite-Lived Intangible Assets, Amortization Expense, Year Four	42,600
Finite-Lived Intangible Assets, Amortization Expense, Year Five	42,300
Intangible assets related to the 2017 Merger [Member]
Schedule of Finite-Lived Intangible Assets Amortization Expense [Line Items]
Amortization of Intangible Assets	$ 41,375	12,872	0
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	19 years 10 months 24 days
Amortization related to other intangible assets [Member]
Schedule of Finite-Lived Intangible Assets Amortization Expense [Line Items]
Amortization of Intangible Assets	$ 1,209	$ 500	$ 500
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	17 years 10 months 24 days

Accrued Payroll and Purchased_3

Accrued Payroll and Purchased Transportation and Accrued Liabilities Accrued Payroll and Purchased Transportation and Accrued Liabilities (Accrued payroll and purchased transportation) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee compensation	[1]	$ 68,121,000	$ 58,438,000
Accrued purchased transportation		58,343,000	48,579,000
Accrued payroll and purchased transportation		126,464,000	107,017,000
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount		$ 1,600
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent		3.00%
Defined Contribution Plan, Cost		$ 8,700,000	3,900,000	$ 1,200,000
Matching contributions liability		$ 6,400,000	$ 6,800,000
Minimum [Member]
Defined Contribution Plan Eligible Age for Employee		18 years
Defined Contribution Plan Employer Contribution Vesting Period		5 years
Maximum [Member]
Defined Contribution Plan Eligible Age for Employee		21 years
Defined Contribution Plan Employer Contribution Vesting Period		6 years
[1]	Accrued payroll includes accruals related to the various 401(k) plans the Company offers to its employees. In order to qualify for these plans, employees must meet the minimum age requirement (18 – 21 years) and have completed six months to one year of service with the Company. Employees' rights to employer contributions are fully vested after five to 6 years from their date of employment. The plans offer discretionary matching contributions capped at either $1,600 annually per employee or 3% of an employee's compensation. The Company's employee benefits expense for matching contributions related to the 401(k) plans was approximately $8.7 million, $3.9 million, and $1.2 million in 2018, 2017, and 2016, respectively. This expense was included in "Salaries, wages, and benefits" in the consolidated income statements. As of December 31, 2018 and 2017, the balance included $6.4 million and $6.8 million, respectively, in respect to matching contributions for the 401(k) plans.

Accrued Payroll and Purchased_4

Accrued Payroll and Purchased Transportation and Accrued Liabilities (Accrued liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Accrued legal	$ 90,789	$ 121,453
Other	60,711	64,926
Accrued liabilities	$ 151,500	$ 186,379

Claims Accruals (Details)

Claims Accruals (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims accruals	$ 361,371	$ 353,429
Less: current portion of claims accruals	(160,044)	(147,285)
Claims accruals – less current portion	201,327	206,144
Auto and collision liability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims accruals	222,004	204,400
Workers' compensation liability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims accruals	120,522	126,563
Owner-operator claims liability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims accruals	12,170	15,236
Cargo damage liability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims accruals	2,998	4,047
Employee medical reserves [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims accruals	$ 3,677	$ 3,183

Claims Accruals Claims Accruals

Claims Accruals Claims Accruals (Self Insurance) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Swift Transportation Company [Member]
Loss Contingencies [Line Items]
Self Insurance Coverage Per Claim	$ 250
Self Insurance Aggregate Coverage	350
Self Insurance Retention	10
Self Insurance Retention Workers Compensation Claims Per Occurrence	5
Knight Transportation Company [Member]
Loss Contingencies [Line Items]
Insurance Aggregate Deductible Amount	2.5
Self Insurance Retention Workers Compensation Claims Per Occurrence	1
Self Retention For Employee Medical Health	0.3
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
Policy Period, March 1, 2018 to March 1, 2019 [Member] | Knight Transportation Company [Member]
Loss Contingencies [Line Items]
Self Insurance Retention	1
Excess Personal Injury And Property Damage Liability Insurance	130
Policy Period, March 1, 2018 to March 1, 2019 [Member] | Knight Transportation Company [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Self Insurance Aggregate Losses	1.6
Policy Period, March 1, 2017 to March 1, 2018 [Member] | Knight Transportation Company [Member]
Loss Contingencies [Line Items]
Self Insurance Retention	1
Policy Period, March 1, 2017 to March 1, 2018 [Member] | Knight Transportation Company [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Self Insurance Aggregate Losses	1.6
Policy Period, March 1, 2016 to March 1, 2017 [Member] | Knight Transportation Company [Member]
Loss Contingencies [Line Items]
Self Insurance Retention	2.5
Policy Period, November 1, 2018 [Member] | Knight Transportation Company [Member]
Loss Contingencies [Line Items]
Excess Personal Injury And Property Damage Liability Insurance	$ 250

Income Taxes (Income Tax Expens

Income Taxes (Income Tax Expense (Benefit) ) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current expense:
Federal	$ 44,357	$ 4,868	$ 43,638
State	22,300	8,337	8,500
Foreign	3,124	133	0
Current expense (benefit), Total	69,781	13,338	52,138
Deferred expense (benefit):
Federal	59,508	(323,326)	6,789
State	1,639	17,731	(1,335)
Foreign	461	541	0
Deferred expense (benefit), Total	61,608	(305,054)	5,454
Income tax expense	$ 131,389	$ (291,716)	$ 57,592

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income tax rate reconciliation [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%	35.00%
Computed expected tax expense	$ 117,478	$ 67,798	$ 53,490
Increase (decrease) in income taxes resulting from:
State income taxes, net of federal income tax benefit	19,256	4,871	4,657
Statutory rate change effect on deferred tax benefit	452	(367,000)	0
Other	(5,797)	2,615	(555)
Income tax expense	$ 131,389	$ (291,716)	$ 57,592

Income Taxes (Components Of Net

Income Taxes (Components Of Net Deferred Tax Asset (Liability) ) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Self-insurance accruals	$ 79,675	$ 70,564
Allowance for doubtful accounts	5,333	5,117
Amortization of stock options	5,325	4,717
Accrued liabilities	27,692	37,654
Vacation accrual	3,499	3,585
Other	8,759	7,227
Total deferred tax assets	130,283	128,864
Valuation allowance	0	0
Total deferred tax assets, net	130,283	128,864
Deferred tax liabilities:
Property and equipment, principally due to differences in depreciation	(503,570)	(429,917)
Prepaid taxes, licenses and permits deducted for tax purposes	(10,933)	(10,217)
Intangible assets	(354,944)	(365,564)
Other	(374)	(2,243)
Deferred tax liabilities	(869,821)	(807,941)
Deferred income taxes	(739,538)	$ (679,077)
State and Local Jurisdiction [Member]
Deferred tax assets:
Valuation allowance	$ 1,300

Income Taxes (Reconciliation Of

Income Taxes (Reconciliation Of Unrecognized Tax Benefits) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Unrecognized tax benefits at beginning of year	$ 7,096	$ 729	$ 0
Increases for tax positions taken prior to beginning of year	1,056	5,432	729
Increases for tax positions taken in the current year	0	935	0
Decreases for tax positions taken prior to beginning of year	729	0	0
Unrecognized tax benefits at end of year	$ 7,423	$ 7,096	$ 729

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, Federal	$ 200
Income Tax Examination, Increase (Decrease) in Liability from Prior Year	0	$ 0
Income Tax Examination, Penalties and Interest Expense	1,400	300	$ 0
Valuation allowance	$ 0	$ 0
Minimum [Member]
Tax Credit Carryforward [Line Items]
Federal and State Operating Loss Carryforwards, Expiration Date	Jan. 1, 2030
Maximum [Member]
Tax Credit Carryforward [Line Items]
Federal and State Operating Loss Carryforwards, Expiration Date	Dec. 31, 2032
State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Valuation allowance	$ 1,300

Income Taxes Income Taxes Other

Income Taxes Income Taxes Other (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Income Tax Disclosure [Abstract]
Cumulative Undistributed Earnings Of Foreign Subsidiaries	$ 75
Minimum [Member]
Income Tax Examination [Line Items]
Income Tax Examination, Year under Examination	2,011
Open Tax Year	2,013
Maximum [Member]
Income Tax Examination [Line Items]
Income Tax Examination, Year under Examination	2,017

Accounts Receivable Securitiz_3

Accounts Receivable Securitization (Detail) - USD ($) $ in Thousands		Jul. 11, 2018	Dec. 31, 2018	Dec. 31, 2017
Schedule of Accounts Receivable Securitization [Line Items]
Program Fees			$ 8,100	$ 2,200
2018 RSA [Member]
Schedule of Accounts Receivable Securitization [Line Items]
Debt Instrument, Issuance 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	[2]	20 to 40 basis points
Program fees on outstanding balances	[3]	one month LIBOR + 80 to 100 basis points
RSA Borrowing Base			325,000
Accounts receivable securitization	[4]		(240,000)
Letters of Credit Outstanding, Amount			(70,900)
Availability under accounts receivable securitization facilities			$ 14,100
2015 RSA [Member]
Schedule of Accounts Receivable Securitization [Line Items]
Debt Instrument, Issuance Date		Dec. 10, 2015
Final maturity date		Jan. 10, 2019
Receivables Sales Agreement, Borrowing Capacity		$ 400,000
Accordion Option Accounts Receivable Securitization	[1]	$ 75,000
Unused commitment fee rate	[2]	35 basis points
Program fees on outstanding balances	[3]	one-month LIBOR + 90 basis points
RSA Borrowing Base				317,600
Accounts receivable securitization	[4]			(305,000)
Letters of Credit Outstanding, Amount				0
Availability under accounts receivable securitization facilities				$ 12,600
Debt Instrument, Interest Rate During Period			3.20%	2.10%
[1]	The accordion option increases the maximum borrowing capacity, subject to participation by the purchasers.
[2]	The 2018 RSA commitment fee rate is based on the percentage of the maximum borrowing capacity utilized.
[3]	The 2018 RSA program fee is based on the Company's consolidated total net leverage ratio.
[4]	Outstanding borrowings are included in "Accounts receivable securitization" in the consolidated balance sheets. Interest accrued on the aggregate principal balance at a rate of 3.2% and 2.1%, as of December 31, 2018 and 2017, respectively.

Debt And Financing Schedule of

Debt And Financing Schedule of Debt Balances by Instrument (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term debt		$ 365,011	$ 364,801
Less: current portion of long-term debt		(421)	(30)
Long-term debt – less current portion		364,590	364,771
Revolving line of credit		195,000	125,000
Long-term debt, including revolving line of credit		560,011	489,801
Debt Issuance Costs, Current, Net		0	0
2017 Agreement, Term Loan [Member]
Debt Instrument [Line Items]
Long-term debt	[1],[2],[3]	364,590	364,355
Debt Issuance Costs, Net		400	600
2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Revolving line of credit		195,000	125,000
Letters of Credit Outstanding, Amount		36,600	153,600
Other
Debt Instrument [Line Items]
Long-term debt		421	446
Line of Credit [Member] | 2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Revolving line of credit	[2],[4]	$ 195,000	$ 125,000
[1]	Net of $0.4 million and $0.6 million deferred loan costs at December 31, 2018 and 2017, respectively.
[2]	Refer to Note 24 for information regarding the fair value of debt.
[3]	The carrying amount of the Term Loan is included in "Long-term debt – less current portion," and is net of $0.4 million and $0.6 million in deferred loan costs as of December 31, 2018 and 2017, respectively.
[4]	The Company also had outstanding letters of credit under the Revolver, primarily related to workers' compensation and self-insurance liabilities of $36.6 million and $153.6 million at December 31, 2018 and 2017, respectively.

Debt And Financing Schedule o_2

Debt And Financing Schedule of Debt Terms (Details) - USD ($)		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Sep. 29, 2017
2017 Agreement, Term Loan [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 400,000,000		$ 400,000,000
Final maturity date				Oct. 2, 2020
Interest rate base				LIBOR
Minimum principal payment — amount				$ 0
Minimum principal payment — frequency				Once
Minimum principal payment — commencement date				Oct. 2, 2020
Debt Instrument, Interest Rate During Period		3.522%	2.694%
2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 800,000,000		$ 800,000,000	$ 1,200,000,000
Final maturity date				Oct. 3, 2022
Interest rate base				LIBOR
Minimum principal payment — amount				$ 0
Minimum principal payment — frequency				Once
Minimum principal payment — commencement date				Oct. 3, 2022
Debt Instrument, Interest Rate During Period		3.448%	2.687%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.10%	0.125%
Line of Credit Facility, Commitment Fee Percentage		1.00%	1.125%
Minimum [Member] | 2017 Agreement, Term Loan [Member]
Debt Instrument [Line Items]
Interest rate margin	[1]	0.88%		0.88%
Minimum [Member] | 2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Interest rate margin	[1]	0.88%		0.88%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage				0.07%
Maximum [Member] | 2017 Agreement, Term Loan [Member]
Debt Instrument [Line Items]
Interest rate margin	[1]	1.50%		1.50%
Maximum [Member] | 2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Interest rate margin	[1],[2]	1.50%		1.50%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage				0.20%
[1]	The interest rate margin for the Term Loan and Revolver is based on the Company's consolidated leverage ratio. As of December 31, 2018, interest accrued at 3.522% on the Term Loan and 3.448% on the Revolver. As of December 31, 2017 interested accrued at 2.694% on the Term Loan and 2.687% on the Revolver.
[2]	The commitment fee for the unused portion of the Revolver is based on the Company's consolidated leverage ratio, and ranges from 0.07% to 0.20%. As of December 31, 2018, commitment fees on the unused portion of the Revolver accrued at 0.100% and outstanding letter of credit fees accrued at 1.000%. As of December 31, 2017, commitment fees on the unused portion of the Revolver accrued at 0.125% and outstanding letter of credit fees accrued at 1.125%.

Debt And Financing (Narrative)

Debt And Financing (Narrative) (Details) - USD ($)		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Sep. 29, 2017
Debt Instrument [Line Items]
Revolving line of credit			$ 195,000,000	$ 125,000,000
Repayment of Outstanding Debt Balances, Cash on Hand					$ 3,400,000
2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity			800,000,000		1,200,000,000
Revolving line of credit			195,000,000	125,000,000
Minimum principal payment — amount			0
2017 Agreement, Term Loan [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity			400,000,000
Minimum principal payment — amount			$ 0
Minimum [Member] | 2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Interest rate margin	[1]		0.88%
Minimum [Member] | 2017 Agreement, Term Loan [Member]
Debt Instrument [Line Items]
Interest rate margin	[1]		0.88%
Maximum [Member] | 2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Interest rate margin	[1],[2]		1.50%
Maximum [Member] | 2017 Agreement, Term Loan [Member]
Debt Instrument [Line Items]
Interest rate margin	[1]		1.50%
Line of Credit [Member] | 2013 Knight Agreement [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 300,000,000
Revolving line of credit					0
Line of Credit Facility, Interest Rate During Period				1.40%
Debt Instrument, Interest Rate, Unused Capacity Fee				0.80%
Line of Credit [Member] | 2015 Agreement, Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 600,000,000
Long-term Line of Credit					35,000,000
Line of Credit [Member] | 2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity					800,000,000
Long-term Line of Credit					85,000,000
Revolving line of credit	[3],[4]		$ 195,000,000	$ 125,000,000
Loans Payable [Member] | 2015 Agreement, Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity					680,000,000
Long-term Line of Credit					450,000,000
Loans Payable [Member] | 2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Minimum principal payment — amount		$ 0
Loans Payable [Member] | 2017 Agreement, Term Loan [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity					$ 400,000,000
London Interbank Offered Rate (LIBOR) [Member] | 2017 Agreement, Revolver [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			1.125%
London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member] | 2013 Knight Agreement [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				0.625%
[1]	The interest rate margin for the Term Loan and Revolver is based on the Company's consolidated leverage ratio. As of December 31, 2018, interest accrued at 3.522% on the Term Loan and 3.448% on the Revolver. As of December 31, 2017 interested accrued at 2.694% on the Term Loan and 2.687% on the Revolver.
[2]	The commitment fee for the unused portion of the Revolver is based on the Company's consolidated leverage ratio, and ranges from 0.07% to 0.20%. As of December 31, 2018, commitment fees on the unused portion of the Revolver accrued at 0.100% and outstanding letter of credit fees accrued at 1.000%. As of December 31, 2017, commitment fees on the unused portion of the Revolver accrued at 0.125% and outstanding letter of credit fees accrued at 1.125%.
[3]	Refer to Note 24 for information regarding the fair value of debt.
[4]	The Company also had outstanding letters of credit under the Revolver, primarily related to workers' compensation and self-insurance liabilities of $36.6 million and $153.6 million at December 31, 2018 and 2017, respectively.

Leases (Detail)

Leases (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Leases, Capital [Abstract]
Capital Leases, Net Investment in Direct Financing Leases	$ 154,300	$ 173,700
Accumulated amortization	34,200	9,400
Non Cancelable Operating Leases, Future Minimum Payments Due [Abstract]
2,019	123,380
2,020	79,088
2,021	42,441
2,022	24,693
2,023	11,728
Thereafter	25,403
Future minimum lease payments	306,733
Non Cancelable Capital Leases, Future Minimum Payments Due
2,019	61,285
2,020	15,843
2,021	30,845
2,022	18,528
2,023	1,347
Thereafter	9,572
Future minimum lease payments	137,420
Less: amounts representing interest	(7,921)
Present value of minimum lease payments	129,499
Less: current portion	(58,251)
Capital lease obligations, long-term	71,248	$ 127,132
Operating Leases as Lessor [Abstract]
2,019	54,080
2,020	37,694
2,021	22,991
2,022	8,343
2,023	13
Thereafter	0
Future minimum lease payments receivable	$ 123,121

Purchase Commitments (Details)

Purchase Commitments (Details) $ in Millions	Dec. 31, 2018USD ($)
Capital Addition Purchase Commitments [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	$ 705
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
Capital Addition Purchase Commitments of Tractors [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	662.7
Non revenue equipment purchase commitments [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	5.8
Purchase Obligation, Due in Second and Third Year	0.6
Purchase Obligation, Due in Fourth and Fifth Year	$ 0

Contingencies and Legal Proce_3

Contingencies and Legal Proceedings (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Accrued legal		$ 90,789	$ 121,453
Washington Overtime Class Actions [Member] | Employee Compensation and Pay Practices Matters [Member]
Loss Contingencies [Line Items]
Loss Contingency, Allegations		The plaintiffs allege one or more of the following, pertaining to Washington state-based driving associates: that Swift 1) failed to pay minimum wage; 2) failed to pay overtime; 3) failed to pay all wages due at established pay periods; 4) failed to provide proper meal and rest periods; 5) failed to provide accurate wage statements; and 6) unlawfully deducted from employee wages. The plaintiffs seek unpaid wages, exemplary damages, interest, other costs, and attorneys’ fees.
Loss Contingency, Opinion of Counsel		The parties in the Slack matter have reached a final settlement. Additionally, the parties in the Hedglin matter have reached a final settlement. The likelihood that a loss has been incurred for the Slack and Hedglin matters is probable and estimable, and the loss has accordingly been accrued.
Washington Overtime Class Actions [Member] | Employee Compensation and Pay Practices Matters [Member] | Washington Overtime Class Action [Member]
Loss Contingencies [Line Items]
Loss Contingency, Name of Plaintiff	[1]	Troy Slack (1)
Loss Contingency, Name of Defendant		Swift Transportation Company of Arizona, LLC and Swift Transportation Corporation
Loss Contingency, Lawsuit Filing Date		September 9, 2011
Loss Contingency, Domicile of Litigation		United States District Court for the Western District of Washington
Washington Overtime Class Actions [Member] | Employee Compensation and Pay Practices Matters [Member] | Washington Overtime Class Action 2 [Member]
Loss Contingencies [Line Items]
Loss Contingency, Name of Plaintiff	[1]	Julie Hedglin (1)
Loss Contingency, Name of Defendant		Swift Transportation Company of Arizona, LLC and Swift Transportation Corporation
Loss Contingency, Lawsuit Filing Date		January 14, 2016
Loss Contingency, Domicile of Litigation		United States District Court for the Western District of Washington
California Wage, Meal, and Rest Class Action [Member] | Employee Compensation and Pay Practices Matters [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		The parties have reached a tentative settlement of the matter. As such, the likelihood that a loss has been incurred is probable and estimable, and the loss has accordingly been accrued.
California Wage, Meal, and Rest Class Action [Member] | Employee Compensation and Pay Practices Matters [Member] | California Wage, Meal, and Rest Class Action 1 [Member]
Loss Contingencies [Line Items]
Loss Contingency, Name of Plaintiff	[2]	John Burnell (1)
Loss Contingency, Name of Defendant		Swift Transportation Co., Inc
Loss Contingency, Lawsuit Filing Date		March 22, 2010
Loss Contingency, Domicile of Litigation		United States District Court for the Central District of California
California Wage, Meal, and Rest Class Action [Member] | Employee Compensation and Pay Practices Matters [Member] | California Wage, Meal, and Rest Class Action 2 [Member]
Loss Contingencies [Line Items]
Loss Contingency, Name of Plaintiff	[2]	James R. Rudsell (1)
Loss Contingency, Name of Defendant		Swift Transportation Co. of Arizona, LLC and Swift Transportation Company
Loss Contingency, Lawsuit Filing Date		April 5, 2012
Loss Contingency, Domicile of Litigation		United States District Court for the Central District of California
Ninth Circuit Owner-operator Misclassification Class Actions [Member] | Independent-Contractor Matters [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 FLSA 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, Opinion of Counsel		In January 2017, the district court issued an order finding that the plaintiffs had signed contracts of employment and thus the case could properly proceed in court, instead of arbitration. In February 2019, the parties reached a tentative settlement pending approval by the court. Based on the above, the likelihood that a loss has been incurred is probable and estimable, and the loss has accordingly been accrued.
Ninth Circuit Owner-operator Misclassification Class Actions [Member] | Independent-Contractor Matters [Member] | Ninth circuit owner operator misclassification class action 1 [Member]
Loss Contingencies [Line Items]
Loss Contingency, Name of Plaintiff		Joseph Sheer, Virginia Van Dusen, Jose Motolinia, Vickii Schwalm, Peter Wood (1)
Loss Contingency, Name of Defendant		Swift Transportation Co., Inc., Interstate Equipment Leasing, Inc., Jerry Moyes, and Chad Killebrew
Loss Contingency, Lawsuit Filing Date		December 22, 2009
Loss Contingency, Domicile of Litigation		Unites States District Court of Arizona and Ninth Circuit Court of Appeals
Utah Collective and Individual Arbitration [Member] | Independent-Contractor Matters [Member]
Loss Contingencies [Line Items]
Loss Contingency, Allegations		The plaintiffs allege that the Central Parties (defined below) misclassified independent contractors as independent contractors, instead of employees, in violation of the FLSA and various state laws. The putative class seeks unpaid wages, liquidated damages, interest, other costs, and attorneys' fees.
Loss Contingency, Opinion of Counsel		In October 2016, the arbitrator ruled that approximately 1,300 Central Refrigerated Service, Inc. drivers should have been classified as employees, not independent contractors. The arbitrator ruled that damages could ultimately be assessed in a collective proceeding and denied Swift's motion to decertify the collective proceeding. On April 14, 2017, the parties reached a settlement of the matter. On April 3, 2018, the court granted final approval of the settlement and the Company paid the settlement in the second quarter of 2018.
Utah Collective and Individual Arbitration [Member] | Independent-Contractor Matters [Member] | Utah Collective And Individual Arbitration 1 [Member]
Loss Contingencies [Line Items]
Loss Contingency, Name of Plaintiff		Gabriel Ciluffo, Kevin Shire, and Bryan Ratterree (1)
Loss Contingency, Name of Defendant		Central Refrigerated Service, Inc., Central Leasing, Inc., Jon Isaacson, and Jerry Moyes (the "Central Parties"), as well as Swift Transportation Company
Loss Contingency, Lawsuit Filing Date		June 1, 2012
Loss Contingency, Domicile of Litigation		American Arbitration Association
[1]	Individually and on behalf of all others similarly situated.
[2]	Individually and on behalf of all others similarly situated.

Share Repurchase Plans (Details

Share Repurchase Plans (Details) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 01, 2018
Class of Stock [Line Items]
Common Stock, Conversion Basis		One-for-one	One-for-one
Stock Repurchased and Retired During Period, Value	$ 179,318,000		$ 39,873,000
Knight Repurchase Plan [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased	10
Company shares repurchased, shares		0	1.6
Swift Repurchase Plan, February 22, 2016 [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount	$ 150,000,000
Amount remaining				$ 62,900,000
Stock Repurchased and Retired During Period, Value		$ 0
Knight-Swift Repurchase Plan, June 1, 2018 [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 250,000,000
Amount remaining	$ 70,700,000
Company shares repurchased, shares	5.9
Stock Repurchased and Retired During Period, Value	$ 179,300,000
Parent [Member]
Class of Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 179,318,000
Parent [Member] | Knight Repurchase Plan [Member]
Class of Stock [Line Items]
Stock Repurchased and Retired During Period, Value			$ 39,873,000

Stock-based Compensation Stock-

Stock-based Compensation Stock-based Compensation (2017 Merger Impact) (Details) - USD ($) $ in Thousands	Sep. 08, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense		$ 32,725
Allocated Share-based Compensation Expense		12,387	$ 6,390	$ 4,041
Knight-Swift Merger [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 6,300
Allocated Share-based Compensation Expense			1,000
Equity Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		$ 11,488	$ 6,242	$ 4,041
Equity Awards [Member] | Knight-Swift Merger [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Business Combination, Equity Interest Earned	$ 13,100

Stock-based Compensation (Stock

Stock-based Compensation (Stock-based Compensation Expense) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 12,387		$ 6,390	$ 4,041
Income tax benefit	3,097		2,415	1,515
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,678		1,788	1,734
Restricted Stock Units Excluding Liability Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	8,019		4,004	1,506
Performance Shares Excluding Liability Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,791		450	801
Equity Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	11,488		6,242	4,041
Liability Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 899	[1]	$ 148	$ 0
[1]	Includes awards granted to executive management in November 2017 and November 2018 that ultimately settle in cash upon fulfilling a requisite service period (for restricted stock units) and fulfilling a requisite service period and achieving performance targets (for performance units)

Stock-based Compensation (Compe

Stock-based Compensation (Compensation Costs Not Yet Recognized) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 32,725
Weighted Average Period	2 years 3 months 4 days
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 2,092
Weighted Average Period	1 year 5 months 1 day
Restricted Stock Units Excluding Liability Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 23,803
Weighted Average Period	2 years 2 months 23 days
Performance Shares Excluding Liability Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 3,763
Weighted Average Period	2 years 10 months 6 days
Liability Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 3,067
Weighted Average Period	2 years 4 months 13 days

Stock-based Compensation Stoc_2

Stock-based Compensation Stock-based compensation expense (Stock Awards Granted) (Details) - shares		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted		618,067	886,243	764,221
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted		0	497,421	569,480
Restricted Stock Units Excluding Liability Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted		420,014	266,958	17,000
Performance Shares Excluding Liability Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted		106,785	44,244	177,741
Equity Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted		526,799	808,623	764,221
Liability Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[1],[2]	91,268	77,620	0
Performance units (liability) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted		54,761	46,572
Restricted Stock Units Liability [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted		36,507	31,048
[1]	Includes 36,507 and 31,048 restricted stock units in 2018 and 2017, respectively.
[2]	Includes 54,761 and 46,572 performance units in 2018 and 2017, respectively.

Stock-based Compensation (Summa

Stock-based Compensation (Summary Of Activity Related To Stock Options) (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares Under Option
Stock options outstanding		1,959,291
Granted		618,067	886,243	764,221
Expired		(26,163)
Forfeited		(78,297)
Stock options outstanding		1,321,605	1,959,291
Aggregate number of stock options expected to vest at a future date		558,184
Exercisable		739,264
Weighted Average Exercise Price
Stock options outstanding		$ 25.48
Granted		0
Exercised		20.56
Expired		28.72
Forfeited		30.17
Stock options outstanding		27.13	$ 25.48
Aggregate number of stock options expected to vest at a future date		29.71
Exercisable		$ 25.02
Weighted Average Remaining Contractual Term
Stock options outstanding		2 years 7 months 24 days	3 years 2 months 11 days
Aggregate number of stock options expected to vest at a future date		2 years 8 months 5 days
Exercisable		2 years 7 months 10 days
Aggregate Intrinsic Value
Stock options outstanding	[1]	$ 35,779
Stock options outstanding	[1]	2,690	$ 35,779
Aggregate number of stock options expected to vest at a future date	[1]	160
Exercisable	[1]	$ 2,527
Share Price		$ 25.07	$ 43.72
Swapped shares		3,044
Employee Stock Option [Member]
Shares Under Option
Granted		0	497,421	569,480
[1]	The aggregate intrinsic value was computed using the closing share price on December 31, 2018 of $25.07 and on December 29, 2017 of $43.72, as applicable.

Stock-based Compensation (Weigh

Stock-based Compensation (Weighted Average Assumptions) (Detail) - $ / shares		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Dividend yield	[1]	0.72%	0.99%
Risk-free rate of return	[2]	1.49%	0.90%
Expected volatility	[3]	27.95%	27.91%
Expected term (in years)		3 years 2 months 20 days	2 years 8 months
Weighted average fair value of stock options granted		$ 6.78	$ 4.28
[1]	The dividend yield assumption is based on Knight's historical experience and anticipated future dividend payouts.
[2]	The risk-free interest rate assumption is based on the US Treasury securities at a constant maturity with a maturity period that most closely resembles the expected term of the stock option award.
[3]	Expected volatility of the Company's common stock is determined based on Knight's historical data.

Stock-based Compensation (Sum_2

Stock-based Compensation (Summary Of Exercise Of Stock Options) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of stock options exercised	533,226	[1]	589,020	708,244
Intrinsic value of stock options exercised	$ 11,745		$ 8,792	$ 7,100
Cash received upon exercise of stock options	10,815		13,159	13,188
Income tax benefit	$ 1,685		$ 1,833	$ 1,847
[1]	Includes 3,044 swapped shares which were excluded from the "Common stock issued to employees" activity on the Consolidated Statements of Stockholders' Equity.

Stock-based Compensation (Statu

Stock-based Compensation (Status of Nonvested Stock Options) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Granted	618,067	886,243	764,221
Weighted Average Fair Value
Granted		$ 6.78	$ 4.28
Employee Stock Option [Member]
Shares
Nonvested	1,040,697
Granted	0	497,421	569,480
Vested	(380,059)
Forfeited	(78,297)
Nonvested	582,341	1,040,697
Weighted Average Fair Value
Nonvested at January 1, 2018	$ 5.49
Granted	0
Vested	5.14
Forfeited	5.76
Nonvested at December 31, 2018	$ 5.69	$ 5.49
Total fair value of shares vested	$ 2	$ 1.7	$ 1.4

Stock-based Compensation (Restr

Stock-based Compensation (Restricted Stock Award Grant) (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards granted	618,067	886,243	764,221
RSUs and restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards granted	456,521

Stock-based Compensation Stoc_3

Stock-based Compensation Stock-based Compensation (Rollforward of Nonvested Restricted Stock Awards) (Details) - $ / shares		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Shares
Granted		618,067		886,243	764,221
Weighted Average Fair Value
Granted				$ 6.78	$ 4.28
RSUs and restricted stock
Shares
Nonvested		979,717
Granted		456,521
Vested	[1]	(193,502)
Forfeited		(72,762)
Nonvested		1,169,974	[2]	979,717
Shares withheld for taxes		53,274
Weighted Average Fair Value
Nonvested at January 1, 2018		$ 26.59
Granted		38.07
Vested		24.43
Forfeited		37.98
Nonvested at December 31, 2018		$ 30.14	[2]	$ 26.59
[1]	Includes 53,274 of shares withheld for taxes which were excluded from the "Common stock issued to employees" activity on the Consolidated Statements of Stockholders' Equity.
[2]	The fair value of each restricted stock unit is based on the closing market price on the grant date.

Stock-based Compensation (Rollf

Stock-based Compensation (Rollforward of Nonvested Performance Shares) (Details) - $ / shares		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Granted		618,067	886,243	764,221
Weighted Average Fair Value
Granted			$ 6.78	$ 4.28
Performance units
Shares
Nonvested		147,633
Granted		161,546
Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Earned And Vested Above Target		0
Vested	[1]	0
Forfeited		0
Nonvested		309,179	147,633
Weighted Average Fair Value
Nonvested at January 1, 2018		$ 35.34
Granted		34.34
Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Earned And Vested Above Target, In Period Weighted Average Grant Date Fair Value		0
Vested	[1]	0
Forfeited		0
Nonvested at December 31, 2018		$ 29.50	$ 35.34
[1]	The performance measurement period for performance units granted in 2017 is January 1, 2018 to December 31, 2020 (three full calendar years). These awards will vest one month following the expiration of the performance measurement period. The performance measurement period for performance units granted in 2018 is January 1, 2019 to December 31, 2021 (three full calendar years). These awards will vest one month following the expiration of the performance measurement period.

Stock-based Compensation Stoc_4

Stock-based Compensation Stock-based Compensation (Performance unit fair value assumptions) (Details) - $ / shares		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	[1]		0.72%	0.99%
Expected volatility	[2]		27.95%	27.91%
Risk-free rate of return	[3]		1.49%	0.90%
Expected term (in years)			3 years 2 months 20 days	2 years 8 months
Performance units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	[4]	0.81%	0.59%	0.99%
Expected volatility	[5]	32.30%	31.28%	27.95%
Average peer volatility	[5]	28.61%	28.45%	34.37%
Average peer correlation coefficient	[6]	58.00%	60.00%	60.00%
Risk-free rate of return	[7]	2.80%	1.88%	0.89%
Expected term (in years)	[8]	3 years 1 month 6 days	3 years 25 days	2 years 10 months 2 days
Weighted-average fair value of performance units granted		$ 34.34	$ 40.81	$ 23.89
[1]	The dividend yield assumption is based on Knight's historical experience and anticipated future dividend payouts.
[2]	Expected volatility of the Company's common stock is determined based on Knight's historical data.
[3]	The risk-free interest rate assumption is based on the US Treasury securities at a constant maturity with a maturity period that most closely resembles the expected term of the stock option award.
[4]	The dividend yield, used to project stock price to the end of the performance period, is based on the Knight's historical experience and future expectation of dividend payouts. Total stockholder return is determined assuming that dividends are reinvested in the issuing entity over the performance period, which is mathematically equivalent to utilizing a 0% dividend yield.
[5]	Management (or peer company) estimated volatility using Knight's (or peer company's) historical share price performance over the remaining performance period as of the grant date.
[6]	The correlation coefficients are used to model the way in which each entity tends to move in relation to each other; the correlation assumptions were developed using the same stock price data as the volatility assumptions.
[7]	The risk-free interest rate assumption is based on US Treasury securities at a constant maturity with a maturity period that most closely resembles the expected term of the performance award.
[8]	Since the Monte Carlo Simulation valuation is an open form model that uses an expected life commensurate with the performance period, the expected life of the performance units was assumed to be the period from the grant date to the end of the performance period.

Stock-based Compensation (Narra

Stock-based Compensation (Narrative) (Detail) - USD ($) $ / shares in Units, shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum purchasing power of common stock for an employee during offering period	$ 6,250
Maximum purchasing power of common stock for an employee during a calendar year	$ 25,000
Maximum percent of total voting power or value of all classes of common stock which restricts from participation of ESPP	5.00%
Number of shares purchased by the employees	49
2012 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance	1,400
Employment period for eligibility of employees participation	90 days
Percentage of payroll deductions from employees compensation	15.00%
Percentage of fair market value of the purchase price	95.00%
Weighted-average fair value of the shares purchased	$ 37.53
Number of additional shares authorized for issuance	1,200
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum contractual term for the options granted	10 years	10 years
Vesting rights rate		33.30%
Class A Common Stock [Member] | 2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares remaining available	2,200

Weighted Average Shares Outst_3

Weighted Average Shares Outstanding (Calculation Of Basic And Diluted Earnings Per Share Attributable To Stockholders) (Detail) - shares shares in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Basic weighted average common shares outstanding		177,018	110,657	80,362
Dilutive effect of stock options		981	1,040	866
Diluted weighted average common shares outstanding		177,999	111,697	81,228
Anti-dilutive shares excluded from diluted earnings per share	[1]	47	98	886
[1]	Shares were excluded from the dilutive-effect calculation because the outstanding awards' exercise prices were greater than the average market price the Company's common stock (for 2018 and 2017) and Knight's common stock (for 2016).

Fair Value Measurement (Carryin

Fair Value Measurement (Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) - USD ($) $ in Thousands		Dec. 31, 2018		Dec. 31, 2017
Financial Liabilities:
2017 Agreement: Term Loan, Carrying Value		$ 365,011		$ 364,801
Accounts receivable securitization, Carrying Value		239,606		305,000
Revolving line of credit, Carrying Value		195,000		125,000
2017 Agreement, Term Loan [Member]
Financial Liabilities:
2017 Agreement: Term Loan, Carrying Value	[1],[2],[3]	364,590		364,355
2017 Agreement: Term Loan, Estimated Fair Value		365,000		365,000
Debt Issuance Costs, Net		400		600
2015 RSA [Member]
Financial Liabilities:
Accounts receivable securitization, Carrying Value		0		305,000
Accounts receivable securitization, Estimated Fair Value		0		305,000
2017 Agreement, Revolver [Member]
Financial Liabilities:
Revolving line of credit, Carrying Value		195,000		125,000
Revolving line of credit, Estimated Fair Value		195,000		125,000
2018 RSA [Member]
Financial Liabilities:
Accounts receivable securitization, Carrying Value		239,606	[4]	0
Accounts receivable securitization, Estimated Fair Value		240,000		$ 0
Debt Issuance Costs, Net		$ 400
[1]	Net of $0.4 million and $0.6 million deferred loan costs at December 31, 2018 and 2017, respectively.
[2]	Refer to Note 24 for information regarding the fair value of debt.
[3]	The carrying amount of the Term Loan is included in "Long-term debt – less current portion," and is net of $0.4 million and $0.6 million in deferred loan costs as of December 31, 2018 and 2017, respectively.
[4]	The carrying amount of the 2018 RSA is included in "Accounts receivable securitization," and is net of $0.4 million deferred loan costs as of December 31, 2018

Fair Value Measurement - Recurr

Fair Value Measurement - Recurring Basis (Detail) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	[1]	$ 1,602	$ 1,427
Debt securities – municipal securities	[1]	2,524	1,887
Financial and Nonfinancial Liabilities, Fair Value Disclosure		0	0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds		1,602	1,427
Debt securities – municipal securities		0	0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds		0	0
Debt securities – municipal securities		2,524	1,887
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using Level 3 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds		0	0
Debt securities – municipal securities		0	0
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure		$ 0	$ 0
[1]	The money market funds and debt securities are trading securities and are restricted to meet statutory requirements. The carrying value, included within "Other long-term assets" in the Company's consolidated balance sheets, approximates the estimated fair value.

Fair Value Measurement - Nonrec

Fair Value Measurement - Nonrecurring basis (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure		$ 0		$ 0
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure		0		0
Non-cash impairments of non-operating assets	[1]			(16,746)
Software | Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		0	[2]	0	[1]
Non-cash impairments of non-operating assets	[2]	(550)
Software | Fair Value, Measurements, Nonrecurring [Member] | Fair Value Measurements at Reporting Date Using Level 1 Inputs
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		0	[2]	0	[1]
Software | Fair Value, Measurements, Nonrecurring [Member] | Fair Value Measurements at Reporting Date Using Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		0	[2]	0	[1]
Software | Fair Value, Measurements, Nonrecurring [Member] | Fair Value Measurements at Reporting Date Using Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		0	[2]	0	[1]
Equipment
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure				400
Equipment | Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		2,800	[3]	350	[4]
Non-cash impairments of non-operating assets		(2,248)	[3]	(98)	[4]
Equipment | Fair Value, Measurements, Nonrecurring [Member] | Fair Value Measurements at Reporting Date Using Level 1 Inputs
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		0	[3]	0	[4]
Equipment | Fair Value, Measurements, Nonrecurring [Member] | Fair Value Measurements at Reporting Date Using Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		2,800	[3]	0	[4]
Equipment | Fair Value, Measurements, Nonrecurring [Member] | Fair Value Measurements at Reporting Date Using Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		$ 0	[3]	$ 350	[4]
[1]	The Company terminated the implementation of Swift's ERP system in 2017. The related impairment loss was included in "Impairments" within operating income in the consolidated income statement (within Swift's non-reportable segments).
[2]	During the fourth quarter of 2018, the Company incurred impairment charges related to replaced software systems of $0.6 million.
[3]	During the fourth quarter of 2018, the Company incurred impairment charges related to the Company airplane of $2.2 million. This impairment was allocated between the Knight Trucking and Knight Logistics segments based on each segment’s use of the asset
[4]	Management reassessed the fair value of certain Interstate Equipment Leasing, LLC tractors as of December 31, 2017, which had a total book value of $0.4 million, determining that there was an impairment loss. The impairment loss was included in "Impairments" within operating income in the consolidated income statement (within Swift's non-reportable segments).

Related Party Transactions (Sch

Related Party Transactions (Schedule Of Services Received And Provided By Company) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Receivable		$ 278	$ 292
Payable		20	0
Central Freight Lines, Inc. [Member]
Related Party Transaction [Line Items]
Receivable		254	213
Payable		0	0
SME Industries [Member]
Related Party Transaction [Line Items]
Receivable		24	79
Payable		0	0
Other Affiliated Entities [Member]
Related Party Transaction [Line Items]
Receivable		0	0
Payable		20	0
Freight Services [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift		1,379	436	$ 0
Received by Knight-Swift		0	0	0
Freight Services [Member] | Central Freight Lines, Inc. [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	681	161	0
Received by Knight-Swift	[1]	0	0	0
Freight Services [Member] | SME Industries [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	698	275	0
Received by Knight-Swift	[1]	0	0	0
Facility and Equipment Leases [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift		935	245	0
Received by Knight-Swift		370	92	0
Facility and Equipment Leases [Member] | Central Freight Lines, Inc. [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	916	245	0
Received by Knight-Swift	[1]	370	92	0
Facility and Equipment Leases [Member] | Other Affiliated Entities [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	19	0	0
Received by Knight-Swift	[1]	0	0	0
Other Services [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift		589	2,819	1,433
Received by Knight-Swift		2,590	604	0
Other Services [Member] | Updike Distribution and Logistics [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[2]	554	2,771	1,433
Received by Knight-Swift	[2]	0	0	0
Other Services [Member] | Other Affiliated Entities [Member]
Related Party Transaction [Line Items]
Provided by Knight-Swift	[1]	35	48	0
Received by Knight-Swift	[1]	$ 2,590	$ 604	$ 0
[1]	Entities affiliated with former Board member Jerry Moyes include Central Freight Lines, SME Industries, Compensi Services, and DPF Mobile. Transactions with these entities that are controlled by and/or are otherwise affiliated with Jerry Moyes, include freight services, facility leases, equipment sales, and other services. •Freight Services Provided by Knight-Swift — The Company charges for freight services to each of these companies for transportation services.•Freight Services Received by Knight-Swift — Transportation services received from Central Freight 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 and certain third-party payroll and employee benefits administration services from the identified related parties are included in other services received by the Company. •In conjunction with Swift's September 8, 2016 announcement that Jerry Moyes would retire from his position as Chief Executive Officer effective December 31, 2016, Swift entered into an agreement with Mr. Moyes to memorialize the terms of his retirement, which was assumed by Knight-Swift. Swift contracted with Mr. Moyes to serve as a non-employee consultant from January 1, 2017 through December 31, 2019, during which time Swift will pay Mr. Moyes a monthly consulting fee in cash.The following is a rollforward of the accrued liability for the consulting fees: (In thousands)Accrued consulting fees – Jerry Moyes, balance at December 31, 2017 (1a)$4,450Additions to accrual—Less: payments(2,225)Accrued consulting fees – Jerry Moyes, balance at December 31, 2018 (1a)$2,225 (1a) The balance is included in "Other long-term liabilities" (noncurrent) and "Accrued liabilities" (current) in the consolidated balance sheets, based on the timing of the expected payments
[2]	Knight had an arrangement with Updike Distribution Logistics, LLC, a company that is owned by the father and three brothers of Executive Vice President of Sales and Marketing, James Updike, Jr. The arrangement allowed Updike Distribution Logistics, LLC to purchase fuel from Knight's vendors at cost, plus an administrative fee. The arrangement was terminated during the second quarter of 2018.

Related Party Transactions Jerr

Related Party Transactions Jerry Moyes' Retirement (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
		Sep. 30, 2016	Dec. 31, 2018
Restructuring and Related Activities [Abstract]
Jerry Moyes' restructuring, initiation date		Sep. 8, 2016
Jerry Moyes' restructuring, completion date		Dec. 31, 2019
Rollforward of accrued liability for the consulting fees [Abstract]
Balance at December 31, 2017	[1]		$ 4,450
Additions to accrual			0
Less: payments			(2,225)
Balance at December 31, 2018	[1]		$ 2,225
[1]	The balance is included in "Other long-term liabilities" (noncurrent) and "Accrued liabilities" (current) in the consolidated balance sheets, based on the timing of the expected payments.

Related Party Transactions Rela

Related Party Transactions Related Party Transactions (Jerry Moyes Transaction) (Details) - Jerry Moyes [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)shares
Jerry Moyes share repurchase [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 29.3
Stock Repurchased During Period, Shares | shares	1,173,680
California Land Purchase [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 7.7

Information by Segment, Geogr_3

Information by Segment, Geography, and Customer Concentration Information by Segment, Geography, and Customer Concentration (Segment Descriptions) (Details)	12 Months Ended
	Dec. 31, 2018Segment
Segment Reporting Information [Line Items]
Number of Reportable Segments	6
Knight Trucking [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Description of Products and Services	Knight Trucking — The Knight Trucking segment is comprised of dry van, refrigerated, and drayage operations. Abilene's trucking operations are included beginning March 17, 2018.
Knight Logistics [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Description of Products and Services	The Knight Logistics segment is primarily comprised of brokerage and intermodal operations. Knight also provides logistics freight management and other non-trucking services through its Knight Logistics business. Abilene's logistics operations are included beginning March 17, 2018.
Swift Truckload [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Description of Products and Services	Swift Truckload — The Swift Truckload segment consists of one-way movements over irregular routes throughout the US, Mexico, and Canada.
Swift Dedicated [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Description of Products and Services	Swift Dedicated — The Swift Dedicated segment devotes use of equipment to specific customers and offers tailored solutions under long-term contracts.
Swift Refrigerated [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Description of Products and Services	Swift Refrigerated — The Swift Refrigerated segment primarily consists of shipments for customers that require temperature-controlled trailers. These shipments include one-way movements over irregular routes, as well as dedicated truck operations.
Swift Intermodal [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Description of Products and Services	The Swift Intermodal segment includes revenue generated by moving freight over the rail in Swift's containers and other trailing equipment, combined with revenue for drayage to transport loads between the railheads and customer locations.
Swift Non-Reportable [Member]
Segment Reporting Information [Line Items]
Segment Reporting, Description of All Other Segments	The Swift non-reportable segments include Swift's logistics and freight brokerage services, as well as support services that Swift's subsidiaries provide to customers and independent contractors, including repair and maintenance shop services, equipment leasing and insurance. Certain of Swift's legal settlements and accruals, amortization of intangibles related to the 2017 Merger, and certain other corporate expenses are also included in the non-reportable segments.

Information by Segment (Summary

Information by Segment (Summary Of Financial Information By Segments) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total revenue	$ 1,394,640	$ 1,346,611	$ 1,331,683	$ 1,271,132	$ 1,359,420	$ 521,608	$ 273,243	$ 271,182	$ 5,344,066	$ 2,425,453	$ 1,118,034
Percentage of Revenue									100.00%	100.00%	100.00%
Operating income (loss)	$ 151,945	$ 106,344	$ 91,628	$ 70,732	$ 447,861	$ 4,199	$ 18,259	$ 15,106	$ 569,043	$ 200,630	$ 148,479
Percentage Of Operating Income									100.00%	100.00%	100.00%
Depreciation and amortization of property and equipment									$ 387,505	$ 193,733	$ 115,660
Percentage Of Depreciation									100.00%	100.00%	100.00%
Knight Trucking [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 1,144,125	$ 906,484	$ 900,368
Percentage of Revenue									21.40%	37.40%	80.50%
Operating income (loss)									$ 209,099	$ 92,298	$ 136,229
Percentage Of Operating Income									36.70%	46.00%	91.70%
Depreciation and amortization of property and equipment									$ 121,376	$ 111,536	$ 111,242
Percentage Of Depreciation									31.30%	57.60%	96.20%
Knight Logistics [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 334,108	$ 234,155	$ 226,912
Percentage of Revenue									6.30%	9.70%	20.30%
Operating income (loss)									$ 24,917	$ 12,600	$ 12,250
Percentage Of Operating Income									4.40%	6.30%	8.30%
Depreciation and amortization of property and equipment									$ 4,441	$ 5,089	$ 4,418
Percentage Of Depreciation									1.10%	2.60%	3.80%
Swift Truckload [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 1,680,882	$ 609,112	$ 0
Percentage of Revenue									31.50%	25.10%	0.00%
Operating income (loss)									$ 225,436	$ 74,924	$ 0
Percentage Of Operating Income									39.60%	37.30%	0.00%
Depreciation and amortization of property and equipment									$ 106,901	$ 32,258	$ 0
Percentage Of Depreciation									27.60%	16.70%	0.00%
Swift Dedicated [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 646,057	$ 200,628	$ 0
Percentage of Revenue									12.10%	8.30%	0.00%
Operating income (loss)									$ 81,942	$ 22,410	$ 0
Percentage Of Operating Income									14.40%	11.20%	0.00%
Depreciation and amortization of property and equipment									$ 50,209	$ 14,381	$ 0
Percentage Of Depreciation									13.00%	7.40%	0.00%
Swift Refrigerated [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 819,190	$ 254,102	$ 0
Percentage of Revenue									15.30%	10.50%	0.00%
Operating income (loss)									$ 34,341	$ 13,626	$ 0
Percentage Of Operating Income									6.00%	6.80%	0.00%
Depreciation and amortization of property and equipment									$ 40,724	$ 11,163	$ 0
Percentage Of Depreciation									10.50%	5.80%	0.00%
Swift Intermodal [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 470,165	$ 130,441	$ 0
Percentage of Revenue									8.80%	5.40%	0.00%
Operating income (loss)									$ 30,127	$ 5,977	$ 0
Percentage Of Operating Income									5.30%	3.00%	0.00%
Depreciation and amortization of property and equipment									$ 11,951	$ 3,231	$ 0
Percentage Of Depreciation									3.10%	1.70%	0.00%
Subtotal [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 5,094,527	$ 2,334,922	$ 1,127,280
Percentage of Revenue									95.40%	96.40%	100.80%
Operating income (loss)									$ 605,862	$ 221,835	$ 148,479
Percentage Of Operating Income									106.40%	110.60%	100.00%
Depreciation and amortization of property and equipment									$ 335,602	$ 177,658	$ 115,660
Percentage Of Depreciation									86.60%	91.80%	100.00%
Swift Non-Reportable [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 314,732	$ 115,530	$ 0
Percentage of Revenue									5.80%	4.80%	0.00%
Operating income (loss)									$ (36,819)	$ (21,205)	$ 0
Percentage Of Operating Income									(6.40%)	(10.60%)	0.00%
Depreciation and amortization of property and equipment									$ 51,903	$ 16,075	$ 0
Percentage Of Depreciation									13.40%	8.20%	0.00%
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenue									$ (65,193)	$ (24,999)	$ (9,246)
Percentage of Revenue									(1.20%)	(1.20%)	(0.80%)

Information by Geography (Narra

Information by Geography (Narrative) (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Abstract]
Percentage of foreign operations total revenue	5.00%	5.00%	5.00%
Long lived assets of foreign operations	5.00%	5.00%

Information by Segment, Geogr_4

Information by Segment, Geography, and Customer Concentration Information by Customer Concentration (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage	10.00%	10.00%	10.00%
Sales Revenue, Net [Member] | Major Customer And Its Subsidiaries [Member]
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage	14.60%	12.50%

Quarterly Result of Operation_3

Quarterly Result of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Information [Abstract]
Total revenue	$ 1,394,640	$ 1,346,611	$ 1,331,683	$ 1,271,132	$ 1,359,420	$ 521,608	$ 273,243	$ 271,182	$ 5,344,066	$ 2,425,453	$ 1,118,034
Net income	151,945	106,344	91,628	70,732	447,861	4,199	18,259	15,106	569,043	200,630	148,479
Net income Attributable to Knight-Swift	$ 151,696	$ 105,881	$ 91,323	$ 70,364	$ 447,564	$ 3,881	$ 17,970	$ 14,876	$ 419,264	$ 484,292	$ 93,863
Basic earnings per share	$ 0.87	$ 0.60	$ 0.51	$ 0.39	$ 2.52	$ 0.04	$ 0.22	$ 0.19	$ 2.37	$ 4.38	$ 1.17
Diluted earnings per share	$ 0.86	$ 0.60	$ 0.51	$ 0.39	$ 2.50	$ 0.04	$ 0.22	$ 0.18	$ 2.36	$ 4.34	$ 1.16