Marten Transport (MRTN) 10-K 1 Mar 21 2020 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 15, 2021	Jun. 30, 2020
Document Information [Line Items]
Entity Central Index Key	0000799167
Entity Registrant Name	MARTEN TRANSPORT LTD
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity File Number	0-15010
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	39-1140809
Entity Address, Address Line One	129 Marten Street
Entity Address, City or Town	Mondov
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	54755
City Area Code	715
Local Phone Number	926-4216
Title of 12(b) Security	COMMON STOCK, PAR VALUE
Trading Symbol	MRTN
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Public Float			$ 1,080,744,000
Entity Common Stock, Shares Outstanding		82,705,005

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 66,127	$ 31,461
Trade, less allowances of $348 and $382, respectively	83,426	90,712
Other	4,202	11,055
Prepaid expenses and other	21,903	20,938
Total current assets	175,658	154,166
Property and equipment:
Less accumulated depreciation	(275,950)	(263,843)
Net property and equipment	654,173	640,394
Other noncurrent assets	1,805	2,026
Total assets	831,636	796,586
Current liabilities:
Accounts payable	25,702	22,917
Insurance and claims accruals	39,595	31,729
Accrued and other current liabilities	24,497	21,680
Total current liabilities	89,794	76,326
Deferred income taxes	121,098	122,022
Noncurrent operating lease liabilities	411	649
Total liabilities	211,303	198,997
Commitments and contingencies (Note 16)
Stockholders’ equity:
Preferred stock, $.01 par value per share; 2,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $.01 par value per share; 192,000,000 shares authorized; 82,705,005 shares at December 31, 2020, and 82,055,199 shares at December 31, 2019, issued and outstanding	827	821
Additional paid-in capital	85,070	79,465
Retained earnings	534,436	517,303
Total stockholders’ equity	620,333	597,589
Total liabilities and stockholders’ equity	831,636	796,586
Revenue Equipment [Member]
Property and equipment:
Property and equipment	787,780	764,419
Land and Building [Member]
Property and equipment:
Property and equipment	90,049	88,414
Office Equipment [Member]
Property and equipment:
Property and equipment	$ 52,294	$ 51,404

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Trade, allowance	$ 348	$ 382
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	2,000,000	2,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	192,000,000	192,000,000
Common stock, shares issued (in shares)	82,705,005	82,055,199
Common stock, shares outstanding (in shares)	82,705,005	82,055,199

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating revenue	$ 874,374	$ 843,271	$ 787,594
Operating expenses (income):
Salaries, wages and benefits	300,155	274,156	252,047
Purchased transportation	154,613	158,948	144,611
Fuel and fuel taxes	98,133	121,341	121,633
Supplies and maintenance	47,815	46,737	40,853
Depreciation	102,893	95,137	88,585
Operating taxes and licenses	10,840	10,100	9,473
Insurance and claims	47,454	38,201	38,657
Communications and utilities	8,011	7,709	6,634
Other	21,665	23,124	21,997
Total operating expenses	781,128	766,773	717,246
Operating income	93,246	76,498	70,348
Other	(140)	(1,190)	(681)
Income before income taxes	93,386	77,688	71,029
Income taxes expense	23,886	16,617	16,002
Net income	$ 69,500	$ 61,071	$ 55,027
Basic earnings per common share (in dollars per share)	$ 0.84	$ 0.75	$ 0.67
Diluted earnings per common share (in dollars per share)	0.84	0.74	0.67
Dividends declared per common share (in dollars per share)	$ 0.633	$ 0.513	$ 0.067
Revenue Equipment [Member]
Operating expenses (income):
Gain on disposition of property, plant and equipment	$ (8,733)	$ (8,680)	$ (7,244)
Facility [Member]
Operating expenses (income):
Gain on disposition of property, plant and equipment	$ (1,718)	$ 0	$ 0

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Cumulative Effect, Period of Adoption, Adjustment [Member]Common Stock [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]Additional Paid-in Capital [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2017					81,800,000
Balance at Dec. 31, 2017	$ 0	$ 0	$ 485	$ 485	$ 818	$ 76,413	$ 448,269	$ 525,500
Net income					$ 0	0	55,027	55,027
Repurchase and retirement of common stock (in shares)					(300,000)
Repurchase and retirement of common stock					$ (3)	(3,754)		(3,756)
Repurchase and retirement of common stock							1
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)					200,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards					$ 2	936	0	938
Employee taxes paid in exchange for shares withheld					0	(104)	0	(104)
Share-based payment arrangement compensation expense					0	3,323	0	3,323
Dividends on common stock					$ 0	0	(5,459)	(5,459)
Balance (in shares) at Dec. 31, 2018					81,700,000
Balance at Dec. 31, 2018					$ 817	76,814	498,323	575,954
Net income					$ 0	0	61,071	$ 61,071
Repurchase and retirement of common stock (in shares)								0
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)					355,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards					$ 4	1,618	(2)	$ 1,620
Employee taxes paid in exchange for shares withheld					0	(784)	0	(784)
Share-based payment arrangement compensation expense					0	1,817	0	1,817
Dividends on common stock					$ 0	0	(42,089)	(42,089)
Balance (in shares) at Dec. 31, 2019					82,055,000
Balance at Dec. 31, 2019					$ 821	79,465	517,303	597,589
Net income					$ 0	0	69,500	69,500
Repurchase and retirement of common stock (in shares)					(53)
Repurchase and retirement of common stock					$ (1)	(596)	0	(597)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)					703,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards					$ 7	4,787	(1)	4,793
Employee taxes paid in exchange for shares withheld					0	(437)	0	(437)
Share-based payment arrangement compensation expense					0	1,851	0	1,851
Dividends on common stock					$ 0	0	(52,366)	(52,366)
Balance (in shares) at Dec. 31, 2020					82,705,000
Balance at Dec. 31, 2020					$ 827	$ 85,070	$ 534,436	$ 620,333

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES:
Net income	$ 69,500	$ 61,071	$ 55,027
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	102,893	95,137	88,585
Tires in service amortization	6,575	6,861	6,982
Deferred income taxes	(924)	16,045	5,351
Share-based payment arrangement compensation expense	1,851	1,817	3,323
Equity in loss (earnings) from affiliate	0	155	(493)
Distribution from affiliate	0	0	227
Adoption of accounting standard	0	0	485
Changes in other current operating items:
Receivables	12,726	(13,638)	(8,131)
Prepaid expenses and other	(4,593)	(4,105)	(3,515)
Accounts payable	883	5,259	1,800
Insurance and claims accruals	7,866	3,626	1,926
Accrued and other current liabilities	3,272	(7,088)	9,881
Net cash provided by operating activities	189,598	156,460	154,204
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Disposition of investment in affiliate	0	1,168	0
Other	(39)	(25)	(15)
Net cash used for investing activities	(106,325)	(140,509)	(104,851)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Dividends on common stock	(52,366)	(42,089)	(5,459)
Issuance of common stock from share-based payment arrangement exercises	4,793	1,620	938
Repurchase and retirement of common stock	(597)	0	(3,756)
Employee taxes paid in exchange for shares withheld	(437)	(784)	(104)
Net cash used for financing activities	(48,607)	(41,253)	(8,381)
NET CHANGE IN CASH AND CASH EQUIVALENTS	34,666	(25,302)	40,972
CASH AND CASH EQUIVALENTS:
Beginning of year	31,461	56,763	15,791
End of year	66,127	31,461	56,763
SUPPLEMENTAL NON-CASH DISCLOSURE:
Change in property and equipment not yet paid	3,230	249	(3,604)
Operating lease assets and liabilities acquired	88	1,668	0
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Income taxes	17,980	4,953	9,526
Interest	0	52	50
Revenue Equipment [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of property, plant and equipment	(8,733)	(8,680)	(7,244)
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Property, plant and equipment additions	(166,395)	(184,680)	(161,160)
Proceeds from property, plant and equipment dispositions	64,185	47,745	63,681
Facility [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of property, plant and equipment	(1,718)	0	0
Buildings And Land Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Property, plant and equipment additions	(6,657)	(4,723)	(7,362)
Proceeds from property, plant and equipment dispositions	$ 2,581	$ 6	$ 5

Note 1 - Summary of Significant

Note 1 - Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Significant Accounting Policies [Text Block]	1. Nature of business: five one Principles of consolidation: Cash and cash equivalents: three may not Trade accounts receivable: may may not 30 Property and equipment: Depreciation is computed based on the cost of the asset, reduced by its estimated salvage value, using the straight-line method for financial reporting purposes. We begin depreciating assets in the month that each asset is placed in service and, therefore, is ready for its intended use, and depreciate each asset until it is taken out of service and available for sale. Accelerated methods are used for income tax reporting purposes. Following is a summary of estimated useful lives for financial reporting purposes: Years Tractors 5 Trailers 7 Refrigerated containers 12 Service and other equipment 3 - 15 Buildings and improvements 20 - 40 In 2020, five seven no five seven Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not Tires in service: 2020, 2019 2018. Income taxes: In the ordinary course of business there is inherent uncertainty in quantifying our income tax positions. We assess our income tax positions and record tax benefits for all years subject to examination based upon management’s evaluation of the facts, circumstances, and information available at the reporting dates. For those tax positions where it is more-likely-than- not 50% not not no Insurance and claims: first first Revenue recognition: 606, Revenue from Contracts with Customers January 1, 2018 four We account for revenue of our Intermodal and Brokerage segments and revenue on freight transported by independent contractors within our Truckload and Dedicated segments on a gross basis because we are the principal service provider controlling the promised service before it is transferred to each customer. We are primarily responsible for fulfilling the promise to provide each specified service to each customer. We bear the primary risk of loss in the event of cargo claims by our customers. We also have complete control and discretion in establishing the price for each specified service. Accordingly, all such revenue billed to customers is classified as operating revenue and all corresponding payments to carriers for transportation services we arrange in connection with brokerage and intermodal activities and to independent contractor providers of revenue equipment are classified as purchased transportation expense within our consolidated statements of operations. See Note 17 Our largest customer, Walmart, accounted for 24% of our revenue in 2020 December 31, 2020, 2019 December 31, 2019 2018. second 2020 December 31, 2020, 2019 December 31, 2019 2018. 2020, 2019 2018, Share-based payment arrangement compensation: may 718, Compensation-Stock Compensation Earnings per common share: Segment reporting: 280, Segment Reporting 17 Use of estimates:

Note 2 - Details of Consolidate

Note 2 - Details of Consolidated Balance Sheet Accounts	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Supplemental Balance Sheet Disclosures [Text Block]	2. Prepaid expenses and other: December 31, (In thousands) 2020 2019 License fees $ 5,529 $ 5,321 Tires in service 4,701 4,972 Insurance premiums 3,653 2,356 Parts and tires inventory 3,372 3,394 Contract assets 1,545 1,729 Other 3,103 3,166 $ 21,903 $ 20,938 Accrued and other current liabilities: December 31, (In thousands) 2020 2019 Vacation $ 7,733 $ 6,558 Salaries and wages 7,584 5,438 Accrued expenses 6,299 6,738 Other 2,881 2,946 $ 24,497 $ 21,680

Note 3 - Long-term Debt

Note 3 - Long-term Debt	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Debt Disclosure [Text Block]	3. In August 2018, August 2023. December 31, 2020, December 31, 2019, December 31, 2020. Our credit facility prohibits us from paying, in any fiscal year, stock redemptions and dividends in excess of 25% of our net income from the prior fiscal year. Waivers allowing stock redemptions and dividends in excess of the 25% 2020 2019 November 2020 August 2019, December 31, 2020 2019.

Note 4 - Related Party Transact

Note 4 - Related Party Transactions	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Related Party Transactions Disclosure [Text Block]	4. The following related party transactions occurred during the three December 31, 2020: (a) We purchase fuel and tires and obtain related services from a company in which one 2020, 2019 2018 2020, 2019 2018 December 31, 2020 December 31, 2019. (b) We paid $154,000 in 2020 one not 2019 2018. not December 31, 2020 2019. (c) We provided transportation services to MW Logistics, LLC, or MWL, a 45% owned affiliate through October 31, 2019, 11.

Note 5 - Income Taxes

Note 5 - Income Taxes	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Income Tax Disclosure [Text Block]	5. The components of the income taxes expense (benefit) consisted of the following: (In thousands) 2020 2019 2018 Current: Federal $ 21,312 $ (1,210 ) $ 7,575 State 3,498 1,782 3,076 Total current 24,810 572 10,651 Deferred: Federal (1,557 ) 15,572 5,815 State 633 473 (464 ) Total deferred (924 ) 16,045 5,351 Total expense (benefit) $ 23,886 $ 16,617 $ 16,002 The federal statutory income tax rate is reconciled to the effective income tax rate as follows: 2020 2019 2018 Federal statutory income tax rate 21 % 21 % 21 % Increase in taxes arising from state income taxes, net of federal income tax benefit 4 2 3 Per diem and other non-deductible expenses 1 1 2 Federal tax credits (1 ) (2 ) (2 ) Other, net 1 (1 ) (1 ) Effective tax rate 26 % 21 % 23 % As of December 31, (In thousands) 2020 2019 Deferred tax assets: Reserves and accrued liabilities $ 12,050 $ 9,050 Other 1,768 2,464 13,818 11,514 Deferred tax liabilities: Depreciation 131,650 130,686 Prepaid expenses 3,266 2,850 134,916 133,536 Net deferred tax liability $ 121,098 $ 122,022 We have not December 31, 2020 2019. Our reserves for unrecognized tax benefits were $4.1 million as of December 31, 2020 December 31, 2019. 2020 December 31, 2020 December 31, 2020 2019, 2017

Note 6 - Earnings per Common Sh

Note 6 - Earnings per Common Share	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Earnings Per Share [Text Block]	6. Basic and diluted earnings per common share were computed as follows: (In thousands, except per share amounts) 2020 2019 2018 Numerator: Net income $ 69,500 $ 61,071 $ 55,027 Denominator: Basic earnings per common share - weighted-average shares 82,527 81,945 81,885 Effect of dilutive stock options 637 725 839 Diluted earnings per common share - weighted-average shares and assumed conversions 83,164 82,670 82,724 Basic earnings per common share $ 0.84 $ 0.75 $ 0.67 Diluted earnings per common share $ 0.84 $ 0.74 $ 0.67 Options totaling 266,650, 330,450 and 230,250 equivalent shares were outstanding but were not 2020, 2019 2018, Unvested performance unit awards (see Note 13 2020, 2019 2018, not

Note 7 - Stock Split

Note 7 - Stock Split	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Stock Split Disclosure [Text Block]	7. On August 13, 2020, three two $.01

Note 8 - Share Repurchase Progr

Note 8 - Share Repurchase Program	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Treasury Stock [Text Block]	8. In 2007, one million 10b 18 2015, two million August 2017 five three July 7, 2017. August 2019, August 2020 three two August 13, 2020. not We repurchased and retired 53,064 shares of common stock for $597,000 in the first 2020 fourth 2018. not 2019. December 31, 2020,

Note 9 - Dividends

Note 9 - Dividends	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Dividends [Text Block]	9. In 2010, 2020 December, third fourth first second 2019 September, 2019. 2018 Our ability to pay cash dividends is currently limited by restrictions contained in our revolving credit facility, which prohibits us from paying, in any fiscal year, stock redemptions and dividends in excess of 25% of our net income from the prior fiscal year. Waivers allowing stock redemptions and dividends in excess of the 25% 2020 2019 November 2020 August 2019,

Note 10 - Third Amendment to Am

Note 10 - Third Amendment to Amended and Restated Certificate of Incorporation	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Stockholders' Equity Note Disclosure [Text Block]	10. In May 2018, $.01

Note 11 - Equity Investment

Note 11 - Equity Investment	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Business Combination Disclosure [Text Block]	11. We owned a 45% equity interest in MWL, a third October 31, 2019, first ten 2019 2018,

Note 12 - Leases

Note 12 - Leases	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Lessee, Operating Leases [Text Block]	12. We lease facilities, drop yards, office space, land, chassis and equipment. All leases are classified as operating leases. We do not 12 Some leases include options to renew, with renewal terms that can extend the lease term from six three Management has elected to apply the short-term lease exemption to leases with an initial term of 12 not As of December 31, (in thousands) 2020 2019 Assets: Other noncurrent assets (a) $ 918 $ 1,178 Liabilities: Accrued and other current liabilities 507 529 Noncurrent operating lease liabilities 411 649 Total liabilities $ 918 $ 1,178 (a) Operating lease asset balances at December 31, 2020 2019. The maturity of the operating lease liabilities is as follows: Amount Maturities: 2021 $ 524 2022 202 2023 132 2024 and 2025 116 Total lease payments 974 Adjust to present value (56 ) Total operating lease liabilities $ 918 The weighted-average remaining lease term at December 31, 2020 December 31, 2019 December 31, 2020 December 31, 2019. not Operating lease assets obtained in exchange for lease obligations in 2020 2019 2020 2019. Total operating lease expense for 2020 2019 12

Note 13 - Employee Benefits

Note 13 - Employee Benefits	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Compensation and Employee Benefit Plans [Text Block]	13. Equity Incentive Plans May 2015, 2015 “2015 2015 March 2015. 2015 may December 31, 2020. one five At our 2019 May 7, 2019, 2015 2015 July 2017. On August 13, 2020, three two July 2020, 2015 three two 2015 As of December 31, 2020, 2015 2015 2005 “2005 May 2015. Under the 2005 2015 December 31, 2020, 107,048‐‐ 2005 2005 We use the Black-Scholes option pricing model to calculate the grant-date fair value of option awards. The fair value of service-based option awards granted was estimated as of the date of grant using the following weighted average assumptions: 2020 2019 2018 Expected option life in years (1) 6.0 6.0 6.0 Expected stock price volatility percentage (2) 28 % 28 % 26 % Risk-free interest rate percentage (3) 0.6 % 2.2 % 2.8 % Expected dividend yield (4) 0.80 % 0.58 % 0.48 % Fair value as of the date of grant $ 3.85 $ 3.93 $ 4.13 ( 1 Expected option life – We use historical employee exercise and option expiration data to estimate the expected life assumption for the Black-Scholes grant-date valuation. We believe that this historical data is currently the best estimate of the expected term of a new option. We use a weighted-average expected life for all awards. ( 2 Expected stock price volatility – We use our stock’s historical volatility for the same period of time as the expected life. We have no ( 3 Risk-free interest rate – The rate is based on the U.S. Treasury yield curve in effect at the time of the grant for the same period of time as the expected life. ( 4 Expected dividend yield – The calculation is based on the total expected annual dividend payout divided by the average stock price. Compensation costs associated with service-based option awards with graded vesting are recognized, net of an estimated forfeiture rate, on a straight-line basis over the requisite service period, which is the period between the grant date and the award’s stated vesting term. Service-based option awards become immediately exercisable in full in the event of death or disability and upon a change in control with respect to all options that have been outstanding for at least six In May 2014, 2005 fifth December 31, 2014 December 31 st December 31, 2018, five five 62. May 2014 In May 2015, 2015 2015 December 31, 2015 2019. In May 2016, 2015 2011 2015, 2015 May 2016 August 2016 2016 December 31, 2016 2020. In May 2017, 2015 2016, five ten May 2017 August 2017 2017 December 31, 2017 2021. In May 2018, 2015 2017. May 2018 August 2018 2018 December 31, 2018 2022. December 2018 August 2018, December 31, 2019 2023. In May 2019, 2015 2017. May 2019 2019 December 2019 2023. In May 2020, 2015 2017, 2020 December 31, 2020 2024. On May 5, 2020, May 5, 2021. The fair value of each performance unit is based on the closing market price on the date of grant. We recognize compensation expense for these awards based on the estimated number of units probable of achieving the vesting requirements of the awards, net of an estimated forfeiture rate. The amount of share-based compensation recognized during a period is based on the value of the portion of the awards that are ultimately expected to vest. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. We currently expect, based on an analysis of our historical forfeitures and known forfeitures on existing awards, that approximately 1.25% of unvested outstanding awards will be forfeited each year. This analysis will be re-evaluated quarterly and the forfeiture rate will be adjusted as necessary. Ultimately, the actual expense recognized over the vesting period will only be for those shares that vest. Total share-based compensation expense recorded in 2020 2019 2018 As of December 31, 2020, 2024. Option activity in 2020 Shares Weighted Average Exercise Price Outstanding at December 31, 2019 1,263,513 $ 9.87 Granted 41,500 15.37 Exercised (580,933 ) 8.25 Forfeited (12,300 ) 12.37 Outstanding at December 31, 2020 711,780 $ 11.47 Exercisable at December 31, 2020 379,218 $ 9.97 The 711,780 options outstanding as of December 31, 2020 December 31, 2020 The fair value of options granted in 2020, 2019 2018 2020, 2019 2018 2020, 2019 2018 Nonvested service-based option awards as of December 31, 2020 2020 Shares Weighted Average Grant Date Fair Value Weighted Average Remaining Contractual Life (in Years) Nonvested at December 31, 2019 477,980 $ 3.45 5.1 Granted 41,500 3.85 6.4 Vested (175,818 ) 3.07 3.2 Forfeited (11,100 ) 3.43 4.3 Nonvested at December 31, 2020 332,562 $ 3.71 4.8 The total fair value of options which vested during 2020, 2019 2018 The following table summarizes our nonvested performance unit award activity in 2020: Shares Weighted Average Grant Date Fair Value Nonvested at December 31, 2019 207,179 $ 11.44 Granted 73,205 16.44 Vested (109,304 )(1) 11.79 Forfeited (16,719 ) 7.49 Nonvested at December 31, 2020 154,361 $ 13.99 ( 1 This number of performance unit award shares vested based on our financial performance in 2020 March 2021. 2020 Retirement Savings Plan 401 three 2020 50 50 first fifth may No 2020, 2019 2018. 2020, 2019 2018. Stock Purchase Plans

Note 14 - Termination of Deferr

Note 14 - Termination of Deferred Compensation Plan	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Compensation Related Costs, General [Text Block]	14. In August 2010, Under the terms of the plan, each participant is eligible to defer portions of their base pay, annual bonus, or receipt of common stock otherwise payable under a vested performance unit award. Each participant can elect a fixed distribution date for the participant’s deferral account other than certain required performance unit award deferrals credited to the discretionary account, which will be distributed after the later of the date of the participant’s termination of employment or the date the participant attains age 62. may may not 2005 2015 December 31, 2020, On May 5, 2020, May 5, 2021.

Note 15 - Fair Value of Financi

Note 15 - Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Fair Value Disclosures [Text Block]	15. The carrying amounts of cash equivalents, accounts receivable and accounts payable approximate fair value because of the short maturity of these instruments.

Note 16 - Commitments and Conti

Note 16 - Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Commitments and Contingencies Disclosure [Text Block]	16. We are committed to purchase $107.2 million of new revenue equipment in 2021. 2025. We self-insure, in part, for losses relating to workers’ compensation, auto liability, general liability, cargo and property damage claims, along with employees’ health insurance with varying risk retention levels. We maintain insurance coverage for per-incident and total losses in excess of these risk retention levels in amounts we consider adequate based upon historical experience and our ongoing review, and reserve currently for the estimated cost of the uninsured portion of pending claims. We are also involved in other legal actions that arise in the ordinary course of business. In the opinion of management, based upon present knowledge of the facts, it is remote that the ultimate outcome of any such legal actions will have a material adverse effect upon our long-term financial position or results of operations.

Note 17 - Revenue and Business

Note 17 - Revenue and Business Segments	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Segment Reporting Disclosure [Text Block]	17. We account for our revenue in accordance with FASB ASC 606, Revenue from Contracts with Customers January 1, 2018 four 606. We have strategically transitioned from a refrigerated long-haul carrier to a multifaceted business offering a network of refrigerated and dry truck-based transportation capabilities across our five The primary source of our operating revenue is provided by our Truckload segment through a combination of regional short-haul and medium-to-long-haul full-load transportation services. We transport food and other consumer packaged goods that require a temperature-controlled or insulated environment, along with dry freight, across the United States and into and out of Mexico and Canada. Our agreements with customers are typically for one Our Dedicated segment provides customized transportation solutions tailored to meet each individual customer’s requirements, utilizing temperature-controlled trailers, dry vans and other specialized equipment within the United States. Our agreements with customers range from three five Generally, we are paid by the mile for our Truckload and Dedicated services. We also derive Truckload and Dedicated revenue from fuel surcharges, loading and unloading activities, equipment detention and other accessorial services. The main factors that affect our Truckload and Dedicated revenue are the rate per mile we receive from our customers, the percentage of miles for which we are compensated, the number of miles we generate with our equipment and changes in fuel prices. We monitor our revenue production primarily through average Truckload and Dedicated revenue, net of fuel surcharges, per tractor per week. We also analyze our average Truckload and Dedicated revenue, net of fuel surcharges, per total mile, non-revenue miles percentage, the miles per tractor we generate, our fuel surcharge revenue, our accessorial revenue and our other sources of operating revenue. Our Intermodal segment transports our customers’ freight within the United States utilizing our temperature-controlled trailers and, beginning in September 2019, Our Brokerage segment develops contractual relationships with and arranges for third 2007 Operating results of our MRTN de Mexico business which offers our customers door-to-door service between the United States and Mexico with our Mexican partner carriers is reported within our Truckload and Brokerage segments. Our customer agreements are typically for one three five 606, four four no four one December 31, 2020 2019, 2020 2019. 30 We account for revenue of our Intermodal and Brokerage segments and revenue on freight transported by independent contractors within our Truckload and Dedicated segments on a gross basis, as discussed in our revenue policy note. The following table sets forth for the years indicated our operating revenue and operating income by segment. We do not not (Dollars in thousands) 2020 2019 2018 Operating revenue: Truckload revenue, net of fuel surcharge revenue $ 342,357 $ 329,304 $ 322,324 Truckload fuel surcharge revenue 36,791 48,696 53,016 Total Truckload revenue 379,148 378,000 375,340 Dedicated revenue, net of fuel surcharge revenue 271,550 223,935 187,137 Dedicated fuel surcharge revenue 38,234 42,049 36,715 Total Dedicated revenue 309,784 265,984 223,852 Intermodal revenue, net of fuel surcharge revenue 79,944 77,750 85,572 Intermodal fuel surcharge revenue 8,789 12,644 16,453 Total Intermodal revenue 88,733 90,394 102,025 Brokerage revenue 96,709 108,893 86,377 Total operating revenue $ 874,374 $ 843,271 $ 787,594 Operating income: Truckload $ 39,637 $ 29,666 $ 35,067 Dedicated 40,909 31,245 18,589 Intermodal 5,730 6,612 11,150 Brokerage 6,970 8,975 5,542 Total operating income $ 93,246 $ 76,498 $ 70,348 Truckload segment depreciation expense was $54.7 million, $54.0 million and $52.2 million, Dedicated segment depreciation expense was $41.4 million, $34.6 million and $29.6 million, Intermodal segment depreciation expense was $5.6 million, $5.1 million and $5.5 million, and Brokerage segment depreciation expense was $1.2 million, $1.5 million and $1.3 million, in 2020, 2019 2018,

Note 18 - Measurement of Credit

Note 18 - Measurement of Credit Losses on Financial Instruments	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Credit Loss, Financial Instrument [Text Block]	18. We adopted FASB ASU No. 2016 13, Measurement of Credit Losses on Financial Instruments January 1, 2020. not

Note 19 - Consolidated Statemen

Note 19 - Consolidated Statements of Cash Flows Reclassifications	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Reclassifications [Text Block]	19. Tires in service amortization in our consolidated statements of cash flows has been reclassified to be consistent with the current presentation, resulting in reclassifications from investing to operating activities for 2019 2018

Note 20 - Quarterly Financial D

Note 20 - Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
Quarterly Financial Information [Text Block]	20. The following is a summary of the quarterly results of operations for 2020 2019: 2020 Quarters In thousands, except per share amounts) First Second Third Fourth Operating revenue $ 218,646 $ 212,384 $ 216,011 $ 227,333 Operating income 18,032 25,256 24,400 25,558 Net income 13,718 18,134 18,044 19,604 Basic earnings per common share 0.17 0.22 0.22 0.24 Diluted earnings per common share 0.17 0.22 0.22 0.24 2019 Quarters (In thousands, except per share amounts) First Second Third Fourth Operating revenue $ 199,023 $ 212,090 $ 214,973 $ 217,185 Operating income 17,733 19,944 20,034 18,787 Net income 13,546 15,190 16,587 15,748 Basic earnings per common share 0.17 0.19 0.20 0.19 Diluted earnings per common share 0.16 0.18 0.20 0.19 The sum of the basic and diluted earnings per common share for the 2020 2019

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts and Reserves	12 Months Ended
	Dec. 31, 2020
Notes to Financial Statements
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	SCHEDULE II MARTEN TRANSPORT, LTD. Valuation and Qualifying Accounts and Reserves (In thousands) Balance at Charged to Beginning of Costs and Balance at Description Year Expenses Deductions End of Year Insurance and claims accruals: Year ended December 31, 2020 $ 31,729 $ 64,276 $ (56,410 )(1) $ 39,595 Year ended December 31, 2019 28,103 56,075 (52,449 )(1) 31,729 Year ended December 31, 2018 26,177 56,122 (54,196 )(1) 28,103 Allowance for doubtful accounts: Year ended December 31, 2020 382 220 (254 )(2) 348 Year ended December 31, 2019 348 65 (31 )(2) 382 Year ended December 31, 2018 300 163 (115 )(2) 348 ( 1 Claims payments ( 2 Write-off of bad debts, net of recoveries See report of independent registered public accounting firm.

Significant Accounting Policies

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Consolidation, Policy [Policy Text Block]	Principles of consolidation:
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and cash equivalents: three may not
Receivable [Policy Text Block]	Trade accounts receivable: may may not 30
Property, Plant and Equipment, Policy [Policy Text Block]	Property and equipment: Depreciation is computed based on the cost of the asset, reduced by its estimated salvage value, using the straight-line method for financial reporting purposes. We begin depreciating assets in the month that each asset is placed in service and, therefore, is ready for its intended use, and depreciate each asset until it is taken out of service and available for sale. Accelerated methods are used for income tax reporting purposes. Following is a summary of estimated useful lives for financial reporting purposes: Years Tractors 5 Trailers 7 Refrigerated containers 12 Service and other equipment 3 - 15 Buildings and improvements 20 - 40 In 2020, five seven no five seven Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not
Tires In Service [Policy Text Block]	Tires in service: 2020, 2019 2018.
Income Tax, Policy [Policy Text Block]	Income taxes: In the ordinary course of business there is inherent uncertainty in quantifying our income tax positions. We assess our income tax positions and record tax benefits for all years subject to examination based upon management’s evaluation of the facts, circumstances, and information available at the reporting dates. For those tax positions where it is more-likely-than- not 50% not not no
Internal Replacements of Insurance Contracts, Policy [Policy Text Block]	Insurance and claims: first first
Revenue from Contract with Customer [Policy Text Block]	Revenue recognition: 606, Revenue from Contracts with Customers January 1, 2018 four We account for revenue of our Intermodal and Brokerage segments and revenue on freight transported by independent contractors within our Truckload and Dedicated segments on a gross basis because we are the principal service provider controlling the promised service before it is transferred to each customer. We are primarily responsible for fulfilling the promise to provide each specified service to each customer. We bear the primary risk of loss in the event of cargo claims by our customers. We also have complete control and discretion in establishing the price for each specified service. Accordingly, all such revenue billed to customers is classified as operating revenue and all corresponding payments to carriers for transportation services we arrange in connection with brokerage and intermodal activities and to independent contractor providers of revenue equipment are classified as purchased transportation expense within our consolidated statements of operations. See Note 17 Our largest customer, Walmart, accounted for 24% of our revenue in 2020 December 31, 2020, 2019 December 31, 2019 2018. second 2020 December 31, 2020, 2019 December 31, 2019 2018. 2020, 2019 2018,
Share-based Payment Arrangement [Policy Text Block]	Share-based payment arrangement compensation: may 718, Compensation-Stock Compensation
Earnings Per Share, Policy [Policy Text Block]	Earnings per common share:
Segment Reporting, Policy [Policy Text Block]	Segment reporting: 280, Segment Reporting 17
Use of Estimates, Policy [Policy Text Block]	Use of estimates:

Note 1 - Summary of Significa_2

Note 1 - Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Notes Tables
Property, Plant and Equipment [Table Text Block]	Years Tractors 5 Trailers 7 Refrigerated containers 12 Service and other equipment 3 - 15 Buildings and improvements 20 - 40

Note 2 - Details of Consolida_2

Note 2 - Details of Consolidated Balance Sheet Accounts (Tables)	12 Months Ended
	Dec. 31, 2020
Notes Tables
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Table Text Block]	(In thousands) 2020 2019 License fees $ 5,529 $ 5,321 Tires in service 4,701 4,972 Insurance premiums 3,653 2,356 Parts and tires inventory 3,372 3,394 Contract assets 1,545 1,729 Other 3,103 3,166 $ 21,903 $ 20,938
Schedule of Accrued Liabilities [Table Text Block]	(In thousands) 2020 2019 Vacation $ 7,733 $ 6,558 Salaries and wages 7,584 5,438 Accrued expenses 6,299 6,738 Other 2,881 2,946 $ 24,497 $ 21,680

Note 5 - Income Taxes (Tables)

Note 5 - Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Notes Tables
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	(In thousands) 2020 2019 2018 Current: Federal $ 21,312 $ (1,210 ) $ 7,575 State 3,498 1,782 3,076 Total current 24,810 572 10,651 Deferred: Federal (1,557 ) 15,572 5,815 State 633 473 (464 ) Total deferred (924 ) 16,045 5,351 Total expense (benefit) $ 23,886 $ 16,617 $ 16,002
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	2020 2019 2018 Federal statutory income tax rate 21 % 21 % 21 % Increase in taxes arising from state income taxes, net of federal income tax benefit 4 2 3 Per diem and other non-deductible expenses 1 1 2 Federal tax credits (1 ) (2 ) (2 ) Other, net 1 (1 ) (1 ) Effective tax rate 26 % 21 % 23 %
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	(In thousands) 2020 2019 Deferred tax assets: Reserves and accrued liabilities $ 12,050 $ 9,050 Other 1,768 2,464 13,818 11,514 Deferred tax liabilities: Depreciation 131,650 130,686 Prepaid expenses 3,266 2,850 134,916 133,536 Net deferred tax liability $ 121,098 $ 122,022

Note 6 - Earnings per Common _2

Note 6 - Earnings per Common Share (Tables)	12 Months Ended
	Dec. 31, 2020
Notes Tables
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	(In thousands, except per share amounts) 2020 2019 2018 Numerator: Net income $ 69,500 $ 61,071 $ 55,027 Denominator: Basic earnings per common share - weighted-average shares 82,527 81,945 81,885 Effect of dilutive stock options 637 725 839 Diluted earnings per common share - weighted-average shares and assumed conversions 83,164 82,670 82,724 Basic earnings per common share $ 0.84 $ 0.75 $ 0.67 Diluted earnings per common share $ 0.84 $ 0.74 $ 0.67

Note 12 - Leases (Tables)

Note 12 - Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Notes Tables
Lease, Balance Sheet Classification [Table Text Block]	(in thousands) 2020 2019 Assets: Other noncurrent assets (a) $ 918 $ 1,178 Liabilities: Accrued and other current liabilities 507 529 Noncurrent operating lease liabilities 411 649 Total liabilities $ 918 $ 1,178
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	Amount Maturities: 2021 $ 524 2022 202 2023 132 2024 and 2025 116 Total lease payments 974 Adjust to present value (56 ) Total operating lease liabilities $ 918

Note 13 - Employee Benefits (Ta

Note 13 - Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2020
Notes Tables
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]	2020 2019 2018 Expected option life in years (1) 6.0 6.0 6.0 Expected stock price volatility percentage (2) 28 % 28 % 26 % Risk-free interest rate percentage (3) 0.6 % 2.2 % 2.8 % Expected dividend yield (4) 0.80 % 0.58 % 0.48 % Fair value as of the date of grant $ 3.85 $ 3.93 $ 4.13
Share-based Payment Arrangement, Option, Activity [Table Text Block]	Shares Weighted Average Exercise Price Outstanding at December 31, 2019 1,263,513 $ 9.87 Granted 41,500 15.37 Exercised (580,933 ) 8.25 Forfeited (12,300 ) 12.37 Outstanding at December 31, 2020 711,780 $ 11.47 Exercisable at December 31, 2020 379,218 $ 9.97
Schedule of Nonvested Share Activity [Table Text Block]	Shares Weighted Average Grant Date Fair Value Weighted Average Remaining Contractual Life (in Years) Nonvested at December 31, 2019 477,980 $ 3.45 5.1 Granted 41,500 3.85 6.4 Vested (175,818 ) 3.07 3.2 Forfeited (11,100 ) 3.43 4.3 Nonvested at December 31, 2020 332,562 $ 3.71 4.8
Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]	Shares Weighted Average Grant Date Fair Value Nonvested at December 31, 2019 207,179 $ 11.44 Granted 73,205 16.44 Vested (109,304 )(1) 11.79 Forfeited (16,719 ) 7.49 Nonvested at December 31, 2020 154,361 $ 13.99

Note 17 - Revenue and Busines_2

Note 17 - Revenue and Business Segments (Tables)	12 Months Ended
	Dec. 31, 2020
Notes Tables
Schedule of Segment Reporting Information, by Segment [Table Text Block]	(Dollars in thousands) 2020 2019 2018 Operating revenue: Truckload revenue, net of fuel surcharge revenue $ 342,357 $ 329,304 $ 322,324 Truckload fuel surcharge revenue 36,791 48,696 53,016 Total Truckload revenue 379,148 378,000 375,340 Dedicated revenue, net of fuel surcharge revenue 271,550 223,935 187,137 Dedicated fuel surcharge revenue 38,234 42,049 36,715 Total Dedicated revenue 309,784 265,984 223,852 Intermodal revenue, net of fuel surcharge revenue 79,944 77,750 85,572 Intermodal fuel surcharge revenue 8,789 12,644 16,453 Total Intermodal revenue 88,733 90,394 102,025 Brokerage revenue 96,709 108,893 86,377 Total operating revenue $ 874,374 $ 843,271 $ 787,594 Operating income: Truckload $ 39,637 $ 29,666 $ 35,067 Dedicated 40,909 31,245 18,589 Intermodal 5,730 6,612 11,150 Brokerage 6,970 8,975 5,542 Total operating income $ 93,246 $ 76,498 $ 70,348

Note 20 - Quarterly Financial_2

Note 20 - Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Notes Tables
Quarterly Financial Information [Table Text Block]	2020 Quarters In thousands, except per share amounts) First Second Third Fourth Operating revenue $ 218,646 $ 212,384 $ 216,011 $ 227,333 Operating income 18,032 25,256 24,400 25,558 Net income 13,718 18,134 18,044 19,604 Basic earnings per common share 0.17 0.22 0.22 0.24 Diluted earnings per common share 0.17 0.22 0.22 0.24 2019 Quarters (In thousands, except per share amounts) First Second Third Fourth Operating revenue $ 199,023 $ 212,090 $ 214,973 $ 217,185 Operating income 17,733 19,944 20,034 18,787 Net income 13,546 15,190 16,587 15,748 Basic earnings per common share 0.17 0.19 0.20 0.19 Diluted earnings per common share 0.16 0.18 0.20 0.19

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts and Reserves (Tables)	12 Months Ended
	Dec. 31, 2020
Notes Tables
Valuation Allowances and Reserves [Table Text Block]	Balance at Charged to Beginning of Costs and Balance at Description Year Expenses Deductions End of Year Insurance and claims accruals: Year ended December 31, 2020 $ 31,729 $ 64,276 $ (56,410 )(1) $ 39,595 Year ended December 31, 2019 28,103 56,075 (52,449 )(1) 31,729 Year ended December 31, 2018 26,177 56,122 (54,196 )(1) 28,103 Allowance for doubtful accounts: Year ended December 31, 2020 382 220 (254 )(2) 348 Year ended December 31, 2019 348 65 (31 )(2) 382 Year ended December 31, 2018 300 163 (115 )(2) 348

Note 1 - Summary of Significa_3

Note 1 - Summary of Significant Accounting Policies (Details Textual)	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Number of Operating Segments	5
Loss on Deposits Above FDIC Amount	$ 0
Number of Reportable Segments	4
Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Walmart [Member]
Concentration Risk, Percentage	24.00%	17.00%	15.00%
Revenue Benchmark [Member] | Customer Concentration Risk [Member] | The Coca-Cola Company [Member]
Concentration Risk, Percentage	12.00%	14.00%	13.00%
Revenue Benchmark [Member] | Geographic Concentration Risk [Member] | UNITED STATES
Concentration Risk, Percentage	99.00%	99.00%	99.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Walmart [Member]
Concentration Risk, Percentage	24.00%	21.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | The Coca-Cola Company [Member]
Concentration Risk, Percentage	8.00%	9.00%
Uninsured Risk [Member] | Auto Liability Claim [Member]
Loss Contingency Range Possible Loss Per Claim	$ 1,000,000
Uninsured Risk [Member] | Workers Compensation Liability Claim [Member]
Loss Contingency Range Possible Loss Per Claim	750,000
Insurance Claims [Member]
Letters of Credit Outstanding, Amount	17,000,000	$ 15,700,000
Supplies and Maintenance Costs [Member]
Amortization, Total	$ 6,600,000	$ 6,900,000	$ 7,000,000
Tractor [Member]
Replacement Of Equipment Period After Purchase (Year)	4 years 1 month 6 days
Property, Plant and Equipment, Useful Life (Year)	5 years
Property, Plant and Equipment, Salvage Value, Percentage	25.00%
Trailer [Member]
Replacement Of Equipment Period After Purchase (Year)	6 years 4 months 24 days
Property, Plant and Equipment, Useful Life (Year)	7 years
Property, Plant and Equipment, Salvage Value, Percentage	35.00%
Refrigerated Containers [Member]
Property, Plant and Equipment, Useful Life (Year)	12 years
Property, Plant and Equipment, Salvage Value, Percentage	0.00%
Tires In Service [Member]
Property, Plant and Equipment, Useful Life (Year)	24 months

Note 1 - Summary of Significa_4

Note 1 - Summary of Significant Accounting Policies - Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2020
Tractor [Member]
Property, Plant and Equipment, Useful Life (Year)	5 years
Trailer [Member]
Property, Plant and Equipment, Useful Life (Year)	7 years
Refrigerated Containers [Member]
Property, Plant and Equipment, Useful Life (Year)	12 years
Service And Other Equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)	3 years
Service And Other Equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)	15 years
Building and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)	20 years
Building and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)	40 years

Note 2 - Details of Consolida_3

Note 2 - Details of Consolidated Balance Sheet Accounts - Prepaid Expenses and Other (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Insurance premiums	$ 3,653	$ 2,356
Contract assets	1,545	1,729
Other	3,103	3,166
Prepaid Expense and Other Assets, Current	21,903	20,938
License Fees Member [Member]
Prepaid expenses	5,529	5,321
Tires In Service [Member]
Prepaid expenses	4,701	4,972
Parts And Tires Inventory [Member]
Prepaid expenses	$ 3,372	$ 3,394

Note 2 - Details of Consolida_4

Note 2 - Details of Consolidated Balance Sheet Accounts - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Vacation	$ 7,733	$ 6,558
Salaries and wages	7,584	5,438
Accrued expenses	6,299	6,738
Other	2,881	2,946
Accrued Liabilities, Current, Total	$ 24,497	$ 21,680

Note 3 - Long-term Debt (Detail

Note 3 - Long-term Debt (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2020	Nov. 30, 2020	Dec. 31, 2019	Aug. 31, 2019	Aug. 31, 2018	Jul. 31, 2018
Line of Credit Facility, Maximum Borrowing Capacity					$ 30,000	$ 40,000
Long-term Line of Credit, Total	$ 0		$ 0
Line of Credit Facility, Remaining Borrowing Capacity	13,000
Line Of Credit Facility Dividend Restrictions Percentage Of Net Income Limit		25.00%		25.00%
Line of Credit Facility, Waiver to Pay Dividends, Maximum		$ 60,000		$ 65,000
Insurance Claims [Member]
Letters of Credit Outstanding, Amount	$ 17,000		$ 15,700
Long-term Debt, Weighted Average Interest Rate, at Point in Time	0.80%

Note 4 - Related Party Transa_2

Note 4 - Related Party Transactions (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 31, 2019
Accounts Payable, Related Parties	$ 900	$ 19,000
M W L [Member]
Equity Method Investment, Ownership Percentage				45.00%
Construction Projects [Member] | Director [Member]
Related Party Transaction, Amounts of Transaction	154,000	0	$ 0
Accounts Payable, Related Parties	0	0
Purchase of Fuel, Tires and Related Services [Member]
Related Party Transaction, Amounts of Transaction	241,000	392,000	341,000
Tire Purchases [Member]
Related Party Transaction, Amounts of Transaction	$ 2,000,000	$ 1,700,000	$ 2,500,000

Note 5 - Income Taxes (Details

Note 5 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Unrecognized Tax Benefits, Ending Balance	$ 4,100,000	$ 3,000,000
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	1,100,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	4,000,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense, Total	$ 12,000	$ 13,000
Domestic Tax Authority [Member]
Open Tax Year	2017 2018 2019 2020

Note 5 - Income Taxes - Compone

Note 5 - Income Taxes - Components of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ 21,312	$ (1,210)	$ 7,575
State	3,498	1,782	3,076
Total current	24,810	572	10,651
Deferred:
Federal	(1,557)	15,572	5,815
State	633	473	(464)
Total deferred	(924)	16,045	5,351
Total expense (benefit)	$ 23,886	$ 16,617	$ 16,002

Note 5 - Income Taxes - Federal

Note 5 - Income Taxes - Federal Income Tax Reconciled to the Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Federal statutory income tax rate	21.00%	21.00%	21.00%
Increase in taxes arising from state income taxes, net of federal income tax benefit	4.00%	2.00%	3.00%
Per diem and other non-deductible expenses	1.00%	1.00%	2.00%
Federal tax credits	(1.00%)	(2.00%)	(2.00%)
Other, net	1.00%	(1.00%)	(1.00%)
Effective tax rate	26.00%	21.00%	23.00%

Note 5 - Income Taxes - Net Def

Note 5 - Income Taxes - Net Deferred Tax Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Reserves and accrued liabilities	$ 12,050	$ 9,050
Other	1,768	2,464
Deferred Tax Assets, Gross, Total	13,818	11,514
Deferred tax liabilities:
Depreciation	131,650	130,686
Prepaid expenses	3,266	2,850
Deferred Tax Liabilities, Gross, Total	134,916	133,536
Net deferred tax liability	$ 121,098	$ 122,022

Note 6 - Earnings per Common _3

Note 6 - Earnings per Common Share (Details Textual) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	266,650	330,450	230,250
Unvested Performance Unit Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	46,705	104,454	2,457

Note 6 - Earnings per Common _4

Note 6 - Earnings per Common Share - Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income	$ 19,604	$ 18,044	$ 18,134	$ 13,718	$ 15,748	$ 16,587	$ 15,190	$ 13,546	$ 69,500	$ 61,071	$ 55,027
Denominator:
Basic earnings per common share - weighted-average shares (in shares)									82,527	81,945	81,885
Effect of dilutive stock options (in shares)									637	725	839
Diluted earnings per common share - weighted-average shares and assumed conversions (in shares)									83,164	82,670	82,724
Basic earnings per common share (in dollars per share)	$ 0.24	$ 0.22	$ 0.22	$ 0.17	$ 0.19	$ 0.20	$ 0.19	$ 0.17	$ 0.84	$ 0.75	$ 0.67
Diluted earnings per common share (in dollars per share)	$ 0.24	$ 0.22	$ 0.22	$ 0.17	$ 0.19	$ 0.20	$ 0.18	$ 0.16	$ 0.84	$ 0.74	$ 0.67

Note 7 - Stock Split (Details T

Note 7 - Stock Split (Details Textual)	Aug. 13, 2020$ / shares	Jul. 07, 2017	Dec. 31, 2020$ / shares	Dec. 31, 2019$ / shares	May 31, 2018$ / shares
Common Stock, Par or Stated Value Per Share (in dollars per share)			$ 0.01	$ 0.01	$ 0.01
Stock Split To [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	3	5
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01
Stockholders' Equity Note, Stock Split, Dividend Settlement, Percent	50.00%
Stock Split from [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	2	3
Stock Split [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01
Stockholders' Equity Note, Stock Split, Dividend Settlement, Percent	50.00%

Note 8 - Share Repurchase Pro_2

Note 8 - Share Repurchase Program (Details Textual)	Aug. 13, 2020	Jul. 07, 2017	Mar. 31, 2020USD ($)shares	Dec. 31, 2018USD ($)shares	Dec. 31, 2020USD ($)shares	Dec. 31, 2019shares	Dec. 31, 2018USD ($)	Aug. 31, 2020shares	Aug. 31, 2019USD ($)shares	Aug. 15, 2017shares	Nov. 04, 2015USD ($)shares	Dec. 31, 2007shares
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares) | shares								2,700,000	1,800,000	3,300,000	2,000,000	1,000,000
Stock Repurchase Program, Authorized Amount | $									$ 34,000,000		$ 40,000,000
Stock Repurchased and Retired During Period, Shares (in shares) | shares			53,064	300,000		0
Stock Repurchased and Retired During Period, Value | $			$ 597,000	$ 3,800,000	$ 597,000		$ 3,756,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $					$ 33,400,000
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased (in shares) | shares					2,600,000
Stock Split To [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	3	5
Stock Split from [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	2	3

Note 9 - Dividends (Details Tex

Note 9 - Dividends (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended												12 Months Ended
	Dec. 31, 2020	Sep. 30, 2019	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 30, 2020	Aug. 31, 2019
Payments of Ordinary Dividends, Common Stock															$ 52,366	$ 42,089	$ 5,459
Line Of Credit Facility Dividend Restrictions Percentage Of Net Income Limit																		25.00%	25.00%
Line of Credit Facility, Waiver to Pay Dividends, Maximum																		$ 60,000	$ 65,000
Paid Quarterly [Member]
Payments of Ordinary Dividends, Common Stock															$ 52,400
Common Stock, Dividends, Per Share, Declared (in dollars per share)	$ 0.50		$ 0.04	$ 0.04	$ 0.027	$ 0.027	$ 0.02	$ 0.02	$ 0.02	$ 0.02	$ 0.017	$ 0.017	$ 0.017	$ 0.017
Special Dividend [Member]
Common Stock, Dividends, Per Share, Declared (in dollars per share)		$ 0.433

Note 10 - Third Amendment to _2

Note 10 - Third Amendment to Amended and Restated Certificate of Incorporation (Details Textual) - $ / shares	Dec. 31, 2020	Dec. 31, 2019	May 31, 2018	Apr. 30, 2018
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Common Stock, Shares Authorized (in shares)	192,000,000	192,000,000	192,000,000	96,000,000

Note 11 - Equity Investment (De

Note 11 - Equity Investment (Details Textual) - M W L [Member] - USD ($) $ in Millions	Oct. 31, 2019	Oct. 31, 2019	Dec. 31, 2018
Equity Method Investment, Ownership Percentage	45.00%	45.00%
Equity Method Investment, Amount Sold	$ 1.3
Equity Method Investment, Ownership Percentage by Non-related Party	55.00%	55.00%
Revenue from Related Parties		$ 2.2	$ 5.5

Note 12 - Leases (Details Textu

Note 12 - Leases (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating Lease, Weighted Average Remaining Lease Term (Year)	30 years	37 months
Operating Lease, Weighted Average Discount Rate, Percent	2.10%	2.40%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 88,000	$ 533,000
Operating Lease, Payments	591,000	579,000
Other Operating Income (Expense) [Member]
Operating Lease, Cost	3,000,000	1,900,000
Short-term Lease, Cost	$ 2,400,000	$ 1,300,000
Minimum [Member]
Lessee, Operating Lease, Renewal Term (Month)	6 months
Maximum [Member]
Lessee, Operating Lease, Renewal Term (Month)	3 years

Note 12 - Leases - Operating Le

Note 12 - Leases - Operating Leases Balance Sheet Information (Details) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019
Noncurrent operating lease liabilities		$ 411	$ 649
Other Noncurrent Assets [Member]
Other noncurrent assets (a)	[1]	918	1,178
Accrued and Other Current Liabilities [Member]
Accrued and other current liabilities		507	529
Other Noncurrent Liabilities [Member]
Noncurrent operating lease liabilities		411	649
Other Liabilities [Member]
Total liabilities		$ 918	$ 1,178
[1]	Operating lease asset balances at December 31, 2020 and 2019.

Note 12 - Leases - Maturity of

Note 12 - Leases - Maturity of Operating Lease Liabilities (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
2021	$ 524,000
2022	202,000
2023	132,000
2024 and 2025	116,000
Total lease payments	974,000
Adjust to present value	(56,000)
Other Liabilities [Member]
Total operating lease liabilities	$ 918,000	$ 1,178,000

Note 13 - Employee Benefits (De

Note 13 - Employee Benefits (Details Textual)	Aug. 13, 2020$ / sharesshares	May 07, 2019shares	Jul. 07, 2017	May 01, 2014shares	May 31, 2020shares	May 31, 2019shares	Dec. 31, 2018shares	Aug. 31, 2018shares	May 31, 2018$ / sharesshares	Aug. 31, 2017shares	May 31, 2017shares	Aug. 31, 2016shares	May 31, 2016shares	May 31, 2015shares	May 31, 2014shares	May 31, 2015shares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / shares
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted (in shares) | shares																	1,815,956
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares									$ 0.01								$ 0.01	$ 0.01
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Forfeiture Rate Of Unvested Outstanding Awards																	1.25%
Share-based Payment Arrangement, Expense																	$ 1,851,000	$ 1,817,000	$ 3,323,000
Share-based Payment Arrangement, Expense, after Tax																	$ 1,400,000	$ 1,400,000	$ 2,600,000
Allocated Share Based Compensation Expense Net Of Tax Amount Per Basic And Diluted Share (in dollars per share) | $ / shares																	$ 0.02	$ 0.02	$ 0.03
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares) | shares																	711,780	1,263,513
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)																	3 years 9 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value																	$ 3,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in shares) | shares																	379,218
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term (Year)																	2 years 10 months 24 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value																	$ 2,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value																	4,100,000	$ 1,400,000	$ 1,500,000
Proceeds from Stock Options Exercised																	4,800,000	1,600,000	938,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value																	$ 539,000	569,000	547,000
Defined Contribution Plan, Employer Matching Contribution, Percent of Match																	35.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay																	6.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage																	20.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount																	$ 0	0	0
Defined Contribution Plan, Cost																	3,000,000	2,700,000	2,300,000
Retirement Savings Plan, Participants Less Than 50 Years Old [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount																	19,500
Retirement Savings Plan, Participants Over50 Years Old [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount																	$ 26,000
Stock Split To [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	3		5
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares	$ 0.01
Stockholders' Equity Note, Stock Split, Dividend Settlement, Percent	50.00%
Stock Split from [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	2		3
Share-based Payment Arrangement, Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding (in shares) | shares																	107,048
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)				5 years													5 years
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding (in shares) | shares																	604,732
Share-based Compensation Arrangement By Share-based Payment Awards, Annual Service Vesting Percentage				5.00%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value																	$ 1,300,000
Performance Shares [Member] | Awards Paid to Employees Upon Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted (in shares) | shares				27,511	73,205	45,000	3,000	3,000	42,000	3,000	65,013	2,501	32,513			48,750
Performance Shares [Member] | One Half of Awards Paid Immediately Upon Vesting and One Half Credited to Employees' Accounts [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted (in shares) | shares						60,000			68,550		163,754		86,505	87,503
Share-based Compensation Arrangement By Share-based Payment Awards, Annual Service Vesting Percentage											10.00%
Unvested Service Based Option Awards [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																	$ 1,100,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)																	2 years 9 months 18 days
Unvested Performance Unit Awards [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																	$ 2,200,000
Service Based Options [Member]
Shares Granted, Value, Share-based Payment Arrangement, before Forfeiture																	$ 160,000	$ 401,000	$ 957,000
2015 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares) | shares		1,300,000
2015 Equity Incentive Plan [Member] | Stock Split To [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares) | shares	3,950,000
2015 Equity Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award Annual Percentage Of Award Which Vests																	20.00%
2015 Equity Incentive Plan [Member] | Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding (in shares) | shares																	318,711
2015 Equity Incentive Plan [Member] | Full Value Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares) | shares		558,334
The 2005 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted (in shares) | shares															91,002
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares) | shares																	0
The 2005 Stock Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding (in shares) | shares																	0
Minimum [Member] | 2015 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)																	7 years
Maximum [Member] | 2015 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)																	10 years

Note 13 - Employee Benefits - S

Note 13 - Employee Benefits - Stock Options Valuation Assumptions (Details) - $ / shares		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Expected option life in years (Year)	[1]	6 years	6 years	6 years
Expected stock price volatility percentage	[2]	28.00%	28.00%	26.00%
Risk-free interest rate percentage	[3]	0.60%	2.20%	2.80%
Expected dividend yield	[4]	0.80%	0.58%	0.48%
Fair value as of the date of grant (in dollars per share)		$ 3.85	$ 3.93	$ 4.13
[1]	Expected option life – We use historical employee exercise and option expiration data to estimate the expected life assumption for the Black-Scholes grant-date valuation. We believe that this historical data is currently the best estimate of the expected term of a new option. We use a weighted-average expected life for all awards.
[2]	Expected stock price volatility – We use our stock’s historical volatility for the same period of time as the expected life. We have no reason to believe that its future volatility will differ from the past.
[3]	Risk-free interest rate – The rate is based on the U.S. Treasury yield curve in effect at the time of the grant for the same period of time as the expected life.
[4]	Expected dividend yield – The calculation is based on the total expected annual dividend payout divided by the average stock price.

Note 13 - Employee Benefits - O

Note 13 - Employee Benefits - Option Activity (Details)	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Balance, shares (in shares) | shares	1,263,513
Balance, weighted average exercise price (in dollars per share) | $ / shares	$ 9.87
Granted, shares (in shares) | shares	41,500
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 15.37
Exercised, shares (in shares) | shares	(580,933)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 8.25
Forfeited, shares (in shares) | shares	(12,300)
Forfeited, weighted average exercise price (in dollars per share) | $ / shares	$ 12.37
Balance, shares (in shares) | shares	711,780
Balance, weighted average exercise price (in dollars per share) | $ / shares	$ 11.47
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in shares) | shares	379,218
Balance, weighted average exercise price (in dollars per share) | $ / shares	$ 9.97

Note 13 - Employee Benefits - N

Note 13 - Employee Benefits - Non-vested Option Awards Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Granted, shares (in shares)	41,500
Granted, weighted average grant date fair value (in dollars per share)	$ 3.85	$ 3.93	$ 4.13
Forfeited, shares (in shares)	(12,300)
Service Based Options [Member]
Nonvested, shares (in shares)	477,980
Nonvested, weighted average grant date fair value (in dollars per share)	$ 3.45
Nonvested, weighted average remaining contractual life (Year)	4 years 9 months 18 days	5 years 1 month 6 days
Granted, shares (in shares)	41,500
Granted, weighted average grant date fair value (in dollars per share)	$ 3.85
Granted, weighted average remaining contractual life (Year)	6 years 4 months 24 days
Vested, shares (in shares)	(175,818)
Vested, weighted average grant date fair value (in dollars per share)	$ 3.07
Vested, weighted average remaining contractual life (Year)	3 years 2 months 12 days
Forfeited, shares (in shares)	(11,100)
Forfeited, weighted average grant date fair value (in dollars per share)	$ 3.43
Forfeited, weighted average remaining contractual life (Year)	4 years 3 months 18 days
Nonvested, shares (in shares)	332,562	477,980
Nonvested, weighted average grant date fair value (in dollars per share)	$ 3.71	$ 3.45

Note 13 - Employee Benefits -_2

Note 13 - Employee Benefits - Non-vested Performance Unit Award Activity (Details) - Performance Shares [Member]	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Nonvested, shares (in shares) | shares	207,179
Nonvested, weighted average grant date fair value (in dollars per share) | $ / shares	$ 11.44
Granted, shares (in shares) | shares	73,205
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 16.44
Vested, shares (in shares) | shares	(109,304)	[1]
Vested, weighted average grant date fair value (in dollars per share) | $ / shares	$ 11.79
Forfeited, shares (in shares) | shares	(16,719)
Forfeited, weighted average grant date fair value (in dollars per share) | $ / shares	$ 7.49
Nonvested, shares (in shares) | shares	154,361
Nonvested, weighted average grant date fair value (in dollars per share) | $ / shares	$ 13.99
[1]	This number of performance unit award shares vested based on our financial performance in 2020 and was distributed or credited to the Marten Transport, Ltd. Deferred Compensation Plan in March 2021. The fair value of unit award shares that vested in 2020 was $1.3 million.

Note 14 - Termination of Defe_2

Note 14 - Termination of Deferred Compensation Plan (Details Textual) - 2015 Equity Incentive Plan [Member] $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)shares
Deferred Compensation Arrangement with Individual, Shares Issued (in shares) | shares	394,056
Deferred Compensation Arrangement with Individual, Compensation Expense | $	$ 6.8

Note 16 - Commitments and Con_2

Note 16 - Commitments and Contingencies (Details Textual)	Dec. 31, 2020USD ($)
Lessee, Operating Lease, Liability, to be Paid, Total	$ 974,000
Capital Addition Purchase Commitments [Member] | Revenue Equipment [Member]
Purchase Obligation, to be Paid, Year One	$ 107,200,000

Note 17 - Revenue and Busines_3

Note 17 - Revenue and Business Segments (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Number of Operating Segments	5
Number of Reportable Segments	4
Customer Contract Term (Year)	1 year
Capitalized Contract Cost, Impairment Loss	$ 0	$ 0
Prepaid Expenses and Other Current Assets [Member]
Contract with Customer, Asset, after Allowance for Credit Loss, Total	1,500	1,700
Dedicated [Member]
Depreciation, Depletion and Amortization, Total	$ 41,400	34,600	$ 29,600
Dedicated [Member] | Minimum [Member]
Customer Contract Term (Year)	3 years
Dedicated [Member] | Maximum [Member]
Customer Contract Term (Year)	5 years
Truckload [Member]
Depreciation, Depletion and Amortization, Total	$ 54,700	54,000	52,200
Intermodal [Member]
Depreciation, Depletion and Amortization, Total	5,600	5,100	5,500
Brokerage [Member]
Depreciation, Depletion and Amortization, Total	$ 1,200	$ 1,500	$ 1,300

Note 17 - Revenue and Busines_4

Note 17 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating revenue	$ 227,333	$ 216,011	$ 212,384	$ 218,646	$ 217,185	$ 214,973	$ 212,090	$ 199,023	$ 874,374	$ 843,271	$ 787,594
Operating income	$ 25,558	$ 24,400	$ 25,256	$ 18,032	$ 18,787	$ 20,034	$ 19,944	$ 17,733	93,246	76,498	70,348
Truckload [Member]
Operating revenue									379,148	378,000	375,340
Operating income									39,637	29,666	35,067
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue									342,357	329,304	322,324
Truckload [Member] | Fuel Surcharge Revenue [Member]
Operating revenue									36,791	48,696	53,016
Dedicated [Member]
Operating revenue									309,784	265,984	223,852
Operating income									40,909	31,245	18,589
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue									271,550	223,935	187,137
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue									38,234	42,049	36,715
Intermodal [Member]
Operating revenue									88,733	90,394	102,025
Operating income									5,730	6,612	11,150
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue									79,944	77,750	85,572
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue									8,789	12,644	16,453
Brokerage [Member]
Operating revenue									96,709	108,893	86,377
Operating income									$ 6,970	$ 8,975	$ 5,542

Note 19 - Consolidated Statem_2

Note 19 - Consolidated Statements of Cash Flows Reclassifications (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Cash Provided by (Used in) Investing Activities, Total	$ (106,325)	$ (140,509)	$ (104,851)
Reclassification Of Tires In Service Amortization And Operating Leases [Member]
Net Cash Provided by (Used in) Investing Activities, Total		$ 3,300	$ 3,600

Note 20 - Quarterly Financial_3

Note 20 - Quarterly Financial Data (Unaudited) - Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating revenue	$ 227,333	$ 216,011	$ 212,384	$ 218,646	$ 217,185	$ 214,973	$ 212,090	$ 199,023	$ 874,374	$ 843,271	$ 787,594
Operating income	25,558	24,400	25,256	18,032	18,787	20,034	19,944	17,733	93,246	76,498	70,348
Net income	$ 19,604	$ 18,044	$ 18,134	$ 13,718	$ 15,748	$ 16,587	$ 15,190	$ 13,546	$ 69,500	$ 61,071	$ 55,027
Basic earnings per common share (in dollars per share)	$ 0.24	$ 0.22	$ 0.22	$ 0.17	$ 0.19	$ 0.20	$ 0.19	$ 0.17	$ 0.84	$ 0.75	$ 0.67
Diluted earnings per common share (in dollars per share)	$ 0.24	$ 0.22	$ 0.22	$ 0.17	$ 0.19	$ 0.20	$ 0.18	$ 0.16	$ 0.84	$ 0.74	$ 0.67

Schedule II - Valuation and Q_3

Schedule II - Valuation and Qualifying Accounts and Reserves - Valuation Allowances and Reserves (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Insurance and Claims Accruals [Member]
Balance at Beginning of Year		$ 31,729	$ 28,103	$ 26,177
Charged to Costs and Expenses		64,276	56,075	56,122
Deductions	[1]	(56,410)	(52,449)	(54,196)
Balance at End of Year		39,595	31,729	28,103
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
Balance at Beginning of Year		382	348	300
Charged to Costs and Expenses		220	65	163
Deductions	[2]	(254)	(31)	(115)
Balance at End of Year		$ 348	$ 382	$ 348
[1]	Claims payments
[2]	Write-off of bad debts, net of recoveries