Saia (SAIA) 10-K 25 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 22, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	SAIA
Entity Registrant Name	SAIA INC
Entity Central Index Key	1,177,702
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		25,845,102
Entity Public Float			$ 2,077,244,002
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 2,194	$ 4,720
Accounts receivable, less allowances of $4,028 in 2018 and $3,991 in 2017	181,612	170,278
Prepaid expenses	20,621	17,540
Income tax receivable	1,825	3,664
Other current assets	7,121	7,047
Total current assets	213,373	203,249
Property and Equipment, at cost	1,521,341	1,289,994
Less-accumulated depreciation	628,283	554,214
Net property and equipment	893,058	735,780
Goodwill	12,105	12,105
Identifiable Intangibles, net	10,559	11,922
Other Noncurrent Assets	4,648	4,259
Total assets	1,133,743	967,315
Current Liabilities:
Accounts payable	78,994	57,438
Wages, vacation and employees’ benefits	48,116	39,748
Claims and insurance accruals	40,980	35,850
Other current liabilities	23,138	19,807
Current portion of long-term debt	18,082	14,083
Total current liabilities	209,310	166,926
Other Liabilities:
Long-term debt, less current portion	104,777	118,833
Deferred income taxes	86,893	59,423
Claims, insurance and other	36,899	39,639
Total other liabilities	228,569	217,895
Commitments and Contingencies
Stockholders’ Equity:
Preferred stock, $0.001 par value, 50,000 shares authorized, none issued and outstanding
Common stock, $0.001 par value, 50,000,000 shares authorized, 25,693,651 and 25,551,617 shares issued and outstanding at December?31, 2018 and 2017, respectively	26	26
Additional paid-in-capital	254,738	246,454
Deferred compensation trust, 143,614 and 170,310 shares of common stock at cost at December?31, 2018 and 2017, respectively	(3,381)	(3,486)
Retained earnings	444,481	339,500
Total stockholders’ equity	695,864	582,494
Total liabilities and stockholders’ equity	$ 1,133,743	$ 967,315

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Allowance of accounts receivable	$ 4,028	$ 3,991
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	50,000	50,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	25,693,651	25,551,617
Common stock, shares outstanding	25,693,651	25,551,617
Deferred compensation trust	143,614	170,310

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Operating Revenue	$ 1,653,849	$ 1,404,703	$ 1,250,391
Operating Expenses:
Salaries, wages and employees’ benefits	872,722	766,790	696,046
Purchased transportation	123,904	107,702	88,239
Fuel, operating expenses and supplies	325,000	268,090	230,364
Operating taxes and licenses	50,089	43,330	40,025
Claims and insurance	38,425	37,162	39,625
Depreciation and amortization	102,153	87,102	76,240
Operating (gains) losses, net	379	(183)	716
Total operating expenses	1,512,672	1,309,993	1,171,255
Operating Income	141,177	94,710	79,136
Nonoperating Expenses (Income):
Interest expense	5,418	5,051	4,394
Other, net	(74)	(92)	(177)
Nonoperating expenses, net	5,344	4,959	4,217
Income Before Income Taxes	135,833	89,751	74,919
Income Tax Expense (Benefit)	30,852	(1,378)	26,895
Net Income	$ 104,981	$ 91,129	$ 48,024
Weighted average common shares outstanding – basic	25,762	25,518	25,038
Weighted average common shares outstanding – diluted	26,291	26,086	25,680
Basic Earnings Per Share	$ 4.08	$ 3.57	$ 1.92
Diluted Earnings Per Share	$ 3.99	$ 3.49	$ 1.87

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Deferred Compensation Trust [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2015	$ 427,863	$ 25	$ 230,593	$ (3,102)	$ 200,347
Beginning Balance, Shares at Dec. 31, 2015		25,141,799
Stock compensation, including options and long-term incentives	3,562		3,562
Stock compensation, including options and long-term incentives, Shares		12,358
Director deferred share activity	1,037		1,037
Exercise of stock options	3,173		3,173
Exercise of stock options, Shares		124,065
Shares issued for long-term incentive awards, net of shares withheld for taxes, Shares		44,479
Shares issued for long-term incentive awards, net of shares withheld for taxes	(651)		(651)
Deferred tax adjustment for long-term incentive plan	44		44
Purchase of shares by Deferred Compensation Trust	(203)		88	(291)
Sale of shares by Deferred Compensation Trust	203			203
Net income	48,024				48,024
Ending Balance at Dec. 31, 2016	483,052	$ 25	237,846	(3,190)	248,371
Ending Balance, Shares at Dec. 31, 2016		25,322,701
Stock compensation, including options and long-term incentives	4,131		4,131
Stock compensation, including options and long-term incentives, Shares		4,840
Director deferred share activity	952		952
Director deferred share activity , Shares		40,142
Exercise of stock options	4,480	$ 1	4,479
Exercise of stock options, Shares		141,500
Shares issued for long-term incentive awards, net of shares withheld for taxes, Shares		42,434
Shares issued for long-term incentive awards, net of shares withheld for taxes	(1,250)		(1,250)
Purchase of shares by Deferred Compensation Trust	(95)		296	(391)
Sale of shares by Deferred Compensation Trust	95			95
Net income	91,129				91,129
Ending Balance at Dec. 31, 2017	582,494	$ 26	246,454	(3,486)	339,500
Ending Balance, Shares at Dec. 31, 2017		25,551,617
Stock compensation, including options and long-term incentives	4,509		4,509
Stock compensation, including options and long-term incentives, Shares		5,184
Director deferred share activity	1,111		1,111
Exercise of stock options	$ 4,165		4,165
Exercise of stock options, Shares	105,860	103,703
Shares issued for long-term incentive awards, net of shares withheld for taxes, Shares		33,147
Shares issued for long-term incentive awards, net of shares withheld for taxes	$ (1,396)		(1,396)
Purchase of shares by Deferred Compensation Trust	(805)		(105)	(700)
Sale of shares by Deferred Compensation Trust	805			805
Net income	104,981				104,981
Ending Balance at Dec. 31, 2018	$ 695,864	$ 26	$ 254,738	$ (3,381)	$ 444,481
Ending Balance, Shares at Dec. 31, 2018		25,693,651

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)
Tax benefits exercise stock options	$ 407
Common Stock [Member]
Tax benefits exercise stock options	407
Additional Paid-in Capital [Member]
Tax benefits exercise stock options	$ 407

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Net income	$ 104,981	$ 91,129	$ 48,024
Noncash items included in net income:
Depreciation and amortization	102,153	87,102	76,240
Provision for doubtful accounts	1,978	2,634	1,475
Deferred income taxes	27,470	(20,776)	12,780
Loss (gain) from property disposals, net	379	(183)	716
Stock-based compensation	5,619	5,083	4,599
Changes in operating assets and liabilities, net of effects of acquisition:
Accounts receivable	(12,981)	(37,985)	(12,401)
Accounts payable	10,608	6,940	(3,349)
Other working capital items, net	15,537	14,023	13,399
Claims, insurance and other	(2,740)	4,531	(860)
Other, net	3,432	5,348	5,803
Net cash provided by operating activities	256,436	157,846	146,426
Investing Activities:
Acquisition of property and equipment	(223,672)	(186,696)	(119,365)
Proceeds from disposal of property and equipment	1,088	5,172	1,682
Net cash used in investing activities	(222,584)	(181,524)	(117,683)
Financing Activities:
Repayment of revolving credit agreement	(233,888)	(217,914)	(199,820)
Borrowing of revolving credit agreement	210,888	260,914	185,286
Proceeds from stock option exercises	4,165	4,480	3,173
Shares withheld for taxes	(1,396)	(1,250)	(650)
Repayment of senior notes		(7,143)	(7,143)
Repayment of capital leases	(16,147)	(12,228)	(8,174)
Net cash provided by (used in) financing activities	(36,378)	26,859	(27,328)
Net Increase (Decrease) in Cash and Cash Equivalents	(2,526)	3,181	1,415
Cash and cash equivalents, beginning of year	4,720	1,539	124
Cash and cash equivalents, end of year	2,194	4,720	1,539
Non Cash Investing Activities
Equipment financed with capital leases	$ 29,090	$ 35,483	$ 34,683

Description of Business and Sum

Description of Business and Summary of Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Description of Business and Summary of Accounting Policies	1. Description of Business and Summary of Accounting Policies Description of Business Saia, Inc. and its subsidiaries (Saia or the Company) are headquartered in Johns Creek, Georgia. Saia is a leading, less-than-truckload (“LTL”) motor carrier with more than 97% of its revenue historically derived from transporting LTL shipments for customers. In addition to the core LTL services provided in 41 states, the Company also offers customers a wide range of other value-added services, including non-asset truckload, expedited and logistics services across the United States. The Chief Operating Decision Maker is the Chief Executive Officer who manages the business, regularly reviews financial information and allocates resources. The Company has one operating segment. Basis of Presentation The accompanying consolidated financial statements include the accounts of Saia, Inc. and its wholly-owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in the consolidated financial statements. Use of Estimates Management makes estimates and assumptions when preparing the consolidated financial statements in conformity with U.S. generally accepted accounting principles. These estimates and assumptions affect the amounts reported in the consolidated financial statements and footnotes. Actual results could differ from those estimates. Accounting Pronouncements Adopted in 2018 In May 2014, the FASB issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers As a result of the adoption of this standard, the Company changed the presentation of its non-asset truckload business from net revenue to gross revenue and changed the method of recognizing that revenue from upon commencement of the services to over the transit time of the freight as it moves from origin to destination. The Company has consistently applied the accounting policies to all periods presented in these condensed consolidated financial statements. The below tables reflect the effect of the adoption of this standard on the previously reported financial data. Condensed Consolidated Balance Sheet impact: As of December 31, 2017 As of December 31, 2016 As adjusted As originally reported Effect of change As adjusted As originally reported Effect of change (in thousands) Accounts receivable $ 170,278 $ 170,610 $ (332 ) $ 134,926 $ 135,083 $ (157 ) Total current assets 203,249 203,581 (332 ) 166,322 166,479 (157 ) Total assets 967,315 967,647 (332 ) 800,213 800,370 (157 ) Accounts payable 57,438 57,717 (279 ) 45,018 45,149 (131 ) Total current liabilities 166,926 167,205 (279 ) 144,813 144,944 (131 ) Retained earnings 339,500 339,553 (53 ) 248,371 248,397 (26 ) Total stockholders’ equity 582,494 582,547 (53 ) 483,052 483,078 (26 ) Total liabilities and stockholders’ equity 967,315 967,647 (332 ) 800,213 800,370 (157 ) Condensed Consolidated Statement of Operations Impact: For the quarter ended December 31, 2017 For the year ended December 31, 2017 As adjusted As originally reported Effect of change As adjusted As originally reported Effect of change (in thousands, except per share data) Operating revenue $ 360,196 $ 353,251 $ 6,945 $ 1,404,703 $ 1,378,510 $ 26,193 Purchased transportation 28,185 21,270 6,915 107,702 81,482 26,220 Total operating expenses 337,268 330,353 6,915 1,309,993 1,283,773 26,220 Operating income 22,928 22,898 30 94,710 94,737 (27 ) Net income 47,789 47,759 30 91,129 91,156 (27 ) Basic Earnings Per Share 1.87 1.87 — 3.57 3.57 — Diluted Earnings Per Share 1.82 1.82 — 3.49 3.49 — For the year ended December 31, 2016 As adjusted As originally reported Effect of change (in thousands, except per share data) Operating revenue $ 1,250,391 $ 1,218,481 $ 31,910 Purchased transportation 88,239 56,329 31,910 Total operating expenses 1,171,255 1,139,345 31,910 Operating income 79,136 79,136 — Net income 48,024 48,024 — Basic Earnings Per Share 1.92 1.92 — Diluted Earnings Per Share 1.87 1.87 — Condensed Consolidated Statement of Cash Flows impact: For the year ended December 31, 2017 For the year ended December 31, 2016 As adjusted As originally reported Effect of change As adjusted As originally reported Effect of change (in thousands) Net income $ 91,129 $ 91,156 $ (27 ) $ 48,024 $ 48,024 $ — Changes in operating assets and liabilities, net (7,143 ) (7,170 ) 27 2,592 2,592 — Net cash provided by operating activities 157,846 157,846 — 146,426 146,426 — Net decrease in cash and cash equivalents 3,181 3,181 — 1,415 1,415 — Accounting Pronouncements Not Yet Adopted In February 2016, the FASB established Topic 842, Leases Land Easement Practical Expedient for Transition to Topic 842 Codification Improvements to Topic 842, Leases Targeted Improvements The new standard is effective for the Company on January 1, 2019, with early adoption permitted. The Company will adopt the new standard on its effective date. A modified retrospective transition approach is required, applying the new standard to all leases existing at the date of initial application. An entity may choose to use either (1) its effective date or (2) the beginning of the earliest comparative period presented in the financial statements as its date of initial application. If an entity chooses the second option, the transition requirements for existing leases also apply to leases entered into between the date of initial application and the effective date. The entity must also recast its comparative period financial statements and provide the disclosures required by the new standard for the comparative periods. The Company will adopt the new standard on January 1, 2019 and use the effective date as its date of initial application. Consequently, financial information will not be updated and the disclosures required under the new standard will not be provided for dates and periods before January 1, 2019. The new standard provides a number of optional practical expedients in transition. The Company intends to elect the ‘package of practical expedients’, which permits it not to reassess under the new standard its prior conclusions about lease identification, lease classification and initial direct costs. The Company does not expect to elect the use-of-hindsight or the practical expedient pertaining to land easements; the latter not being applicable to it. The Company expects that this standard will have a material effect on its consolidated financial statements. While the Company continues to assess all of the effects of adoption, it currently believes the most significant effects relate to (1) the recognition of new ROU assets and lease liabilities on its consolidated balance sheet for its real estate operating leases and (2) providing significant new disclosures about its leasing activities. The Company does not expect a significant change in its leasing activities between now and the first financial statements issued with adoption. On adoption, the Company currently expects to recognize additional operating liabilities of approximately $70 to $80 million, with corresponding ROU assets of the same amount based on the present value of the remaining minimum rental payments for existing operating leases. The new standard also provides practical expedients for an entity’s ongoing accounting. The Company currently intends to elect the short-term lease recognition exemption for all leases that qualify. This means, for those leases that qualify, the Company will not recognize ROU assets or lease liabilities, and this includes not recognizing ROU assets or lease liabilities for existing short-term leases of those assets in transition. The Company also currently intends to elect the practical expedient to not separate lease and non-lease components for all of its leases other than leases of real estate. Summary of Accounting Policies Major accounting policies and practices used in the preparation of the accompanying consolidated financial statements not covered in other notes to the consolidated financial statements are as follows: Cash and Cash Equivalents and Checks Outstanding: Cash and cash equivalents in excess of current operating requirements are invested in short-term interest bearing instruments purchased with original maturities of three months or less and are stated at cost, which approximates market. Checks outstanding in excess of cash on deposit are classified in accounts payable on the accompanying consolidated balance sheets and in operating activities in the accompanying consolidated statements of cash flows. Parts, fuel and operating supplies: Parts, fuel and operating supplies are carried at average cost and included in other current assets. Property and Equipment Including Repairs and Maintenance: Property and equipment are carried at cost less accumulated depreciation. Depreciation is computed using the straight-line method based on the following service lives: Years Structures 20 to 25 Tractors 6 to 10 Trailers 10 to 14 Other revenue equipment 7 to 14 Technology equipment and software 3 to 5 Other 3 to 10 At December 31, property and equipment consisted of the following (in thousands): 2018 2017 Land $ 100,157 $ 81,487 Structures 321,283 268,723 Tractors 476,875 398,652 Trailers 354,490 305,540 Other revenue equipment 83,571 77,691 Technology equipment and software 110,954 93,754 Other 74,011 64,147 Total property and equipment, at cost $ 1,521,341 $ 1,289,994 Maintenance and repairs are charged to operations while replacements and improvements that extend the asset’s life are capitalized. The Company’s investment in technology equipment and software consists primarily of systems to support customer service, maintenance and freight management. Depreciation was $100.8 million, $85.7 million and $74.5 million for the years ended December 31, 2018, 2017 and 2016, respectively. Depreciation and amortization expense includes amortization of assets under capital lease. At December 31, 2018, trailers acquired under capital leases had a gross carrying value of $132.5 million and accumulated depreciation of $21.6 million. At December 31, 2017, trailers acquired under capital leases had a gross carrying value of $106.3 million and accumulated depreciation of $13.3 million. Computer Software Developed or Obtained for Internal Use: The Company capitalizes certain costs associated with developing or obtaining internal-use software. Capitalizable costs include external direct costs of materials and services utilized in developing or obtaining the software and payroll and payroll-related costs for employees directly associated with the development of the project. For the years ended December 31, 2018, 2017, and 2016, the Company capitalized $1.1 million, $2.1 million, and $1.6 million, respectively, of primarily payroll-related costs. Claims and Insurance Accruals: Claims and insurance accruals, both current and long-term, reflect the estimated cost of claims for workers’ compensation (discounted to present value), cargo loss and damage, and bodily injury and property damage not covered by insurance. These costs are included in claims and insurance expense, except for workers’ compensation, which is included in employees’ benefits expense. The liabilities are included in claims and insurance reserves based on estimates of claims incurred. Liabilities for unsettled claims and claims incurred but not yet reported are actuarially determined with respect to workers’ compensation claims and with respect to all other liabilities, estimated based on management’s evaluation of the nature and severity of individual claims and past experience. For workers’ compensation, the amount of the discount at December 31, 2018 and December 31, 2017 was $5.0 million and $3.5 million, respectively. Risk retention amounts per occurrence during the three years ended December 31, 2018, were as follows: Workers’ compensation $ 1,000,000 Bodily injury and property damage 2,000,000 Employee medical and hospitalization 400,000 Cargo loss and damage 250,000 Effective March 1, 2018, the Company entered into a new auto liability policy with a three-year term. The risk retention amount per occurrence remains at $2.0 million under the new policy. The policy includes a limit for a single loss of $8.0 million, an aggregate loss limit of $24.0 million for each policy year, and a $48.0 million aggregate loss limit for the 36-month term ended March 1, 2021. The policy includes a returnable premium of up to $5.2 million, to be adjusted by the insurer for changes in claims, and a provision to extend the term of the policy for one additional 12-month period, if management and the insurer mutually agree to commute the policy for the first 12 months of the policy term. A decision with respect to commutation of the first 12 months of the policy cannot be made before March 1, 2019. The policy also includes a returnable premium of up to $15.6 million, to be adjusted by the insurer for changes in claims, if management and the insurer mutually agree to commute the policy for the entire 36 months. A decision with respect to commutation of the entire policy cannot be made before August 30, 2021, unless both the Company and the insurance carrier agree to a commutation prior to the end of the policy term. Additionally, the Company may be required to pay an additional premium of up to $11.0 million if paid losses are greater than $15.6 million over the three-year policy period. Based on 2018 claims experience, no such additional premium was accrued at December 31, 2018. As of December 31, 2018, no portion of the policy was eligible for commutation, and insufficient claims experience is available to determine the likelihood of future commutations. As such, no related amounts have been recorded at December 31, 2018. Income Taxes: Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. As required by FASB Accounting Standards Codification (“ASC”) 740, , the Company follows this guidance which defines the threshold for recognizing the benefits of tax-filing positions in the financial statements as “more-likely-than-not” to be sustained by the tax authority. ASC 740 also prescribes a method for computing the tax benefit of such tax positions to be recognized in the financial statements. In addition, it provides guidance on derecognition, classification, interest and penalties, accounting in interim periods, disclosure and transition. Revenue Recognition: The Company’s revenues are derived primarily from the transportation of freight as it satisfies performance obligations that arise from contracts with its customers. The Company’s performance obligations arise when it receives a bill of lading (“BOL”) to transport a customer's commodities at negotiated prices contained in either a transportation services agreement or a publicly disclosed tariff rate. Once a BOL is received, a legally-enforceable contract is formed whereby the parties are committed to perform and the rights of the parties, shipping terms and conditions, and payment terms have been identified. A customer may submit many BOLs for transportation services at various times throughout a service agreement term but each shipment represents a distinct service that is a separately identified performance obligation. The average transit time to complete a shipment is between 1 to 5 days. Payments for transportation services are normally billed after completion of the service and are generally due within 30 days after the invoice date. The Company recognizes revenue related to the Company’s LTL, non-asset truckload and expedited services over the transit time of the shipment as it moves from origin to destination. Revenue for services started but not completed at the reporting date is allocated based on the relative transit time in each reporting period, with the portion allocated for services subsequent to the reporting date considered remaining performance obligations. Key estimates included in the recognition and measurement of revenue and related accounts receivable are as follows: • Revenue associated with shipments in transit is recognized ratably over transit time and is based on average cycle times to move shipments from their origin to their final destination or interchange; and • Adjustments to revenue for billing adjustments and collectability. Revenue related to interline transportation services that involve the services of another party, such as another LTL service provider, is reported on a net basis. The portion of the gross amount billed to customers that is remitted by the Company to another party is not reflected as revenue. Revenue from logistics services is recognized as the services are provided. Remaining performance obligations represent the transaction price allocated to future reporting periods for freight services started but not completed at the reporting date. This includes the unearned portion of billed and unbilled amounts for cancellable freight shipments in transit that the Company expects to recognize as revenue in the period subsequent to the reporting date, which is on average less than one week. The Company has elected to apply the optional exemption in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (ASC) 606 as it pertains to additional quantitative disclosures pertaining to remaining performance obligations. Stock-Based Compensation: The Company accounts for its employee stock-based compensation awards in accordance with ASC 718, . ASC 718 requires that all employee stock-based compensation is recognized as an expense in the financial statements and that for equity-classified awards such expenses are measured at the grant date fair value of the award. Stock options are accounted for in accordance with ASC 718 with the expense amortized over the three-year vesting period using a Black-Scholes-Merton model to estimate the fair value of stock options granted to employees. Restricted stock is accounted for in accordance with ASC 718 with the expense amortized over a three to five year vesting period using the intrinsic valuation method to estimate the fair value of restricted stock awards granted to employees. Stock-based Performance Unit Awards are accounted for in accordance with ASC 718 with the expense amortized over the three-year vesting period using a Monte Carlo model to estimate fair value at the date the awards are granted. Credit Risk: The Company routinely grants credit to its customers. The risk of significant loss in trade receivables is substantially mitigated by the Company’s credit evaluation process, short collection terms, low revenue per transaction and services performed for a large number of customers with no single customer representing more than 5.0 percent of consolidated operating revenue. Allowances for potential credit losses are based on historical loss experience, current economic environment, expected trends and customer specific factors. Impairment of Long-Lived Assets: As required by ASC 360, , long-lived assets, such as property, plant and equipment, and purchased intangible assets subject to amortization, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If circumstances require a long-lived asset or asset group be tested for possible impairment, the Company first compares undiscounted cash flows expected to be generated by that asset or asset group to its carrying value. If the carrying value of the long-lived asset or asset group is not recoverable on an undiscounted cash flow basis, impairment is recognized to the extent that the carrying value exceeds its fair value. Fair value is determined through various valuation techniques including discounted cash flow models, quoted market values and third-party independent appraisals, as deemed necessary. The Company has adopted ASU 2011-08, Testing Goodwill for Impairment Intangibles – Goodwill and Other Advertising: The costs of advertising are expensed as incurred. Advertising costs charged to expense were $3.9 million, $2.2 million, and $1.2 million in 2018, 2017 and 2016, respectively. Financial Instruments The carrying amounts of financial instruments including cash and cash equivalents, accounts receivable, accounts payable and short-term debt approximated fair value as of December 31, 2018 and 2017, because of the relatively short maturity of these instruments. See Note 2 for fair value disclosures related to long-term debt.

Debt and Financing Arrangements

Debt and Financing Arrangements	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt and Financing Arrangements	2. Debt and Financing Arrangements At December 31, debt consisted of the following (in thousands): December 31, 2018 December 31, 2017 Credit Agreement with Banks, described below $ 20,000 $ 43,000 Capital Leases, described below 102,859 89,916 Total debt 122,859 132,916 Less: current portion of long-term debt 18,082 14,083 Long-term debt, less current portion $ 104,777 $ 118,833 The Company's liquidity needs arise primarily from capital investment in new equipment, land and structures, information technology and letters of credit required under insurance programs, as well as funding working capital requirements. The Company is party to a revolving credit agreement (the Existing Credit Agreement) with a group of banks to fund capital investments, letters of credit and working capital needs. The Company has pledged certain land and structures, accounts receivable and other assets to secure indebtedness under this agreement. Credit Agreement The Existing Credit Agreement is a revolving credit facility for up to $250 million expiring in March 2020. The Existing Credit Agreement also has an accordion feature that allows for an additional $75 million in availability, subject to bank approval. The Existing Credit Agreement provides for a LIBOR rate margin range from 112.5 basis points to 225 basis points, base rate margins from minus 12.5 basis points to plus 50 basis points, an unused portion fee from 20 basis points to 30 basis points and letter of credit fees from 112.5 basis points to 225 basis points, in each case based on the Company's leverage ratio. Under the Existing Credit Agreement, the Company must maintain certain financial covenants including a minimum fixed charge coverage ratio and a maximum leverage ratio. The Existing Credit Agreement provides for a pledge by the Company of certain land and structures, accounts receivable and other assets to secure indebtedness under this agreement. At December 31, 2018, the Company had borrowings of $20.0 million and outstanding letters of credit of $27.7 million under the Existing Credit Agreement. At December 31, 2017, the Company had $43.0 million of outstanding borrowings and outstanding letters of credit of $33.9 million under the Existing Credit Agreement. The available portion of the Existing Credit Agreement may be used for general corporate purposes, including capital expenditures, working capital and letter of credit requirements as needed. On February 5, 2019, the Company entered into the Sixth Amended and Restated Credit Agreement with its banking group (as amended, the Amended Credit Agreement). The amendment increased the amount of the revolver from $250 million to $300 million and extended the term until February 2024. The Amended Credit Agreement also has an accordion feature that allows for an additional $100 million availability, subject to bank approval. The amendment reduced the interest rate pricing grid. The Amended Credit Agreement provides for a Capital Leases The Company is obligated under capital leases with seven year terms which include obligations covering revenue equipment totaling $102.9 million and $89.9 million as of December 31, 2018 and 2017, respectively. Amortization of assets held under the capital leases is included in depreciation and amortization expense. The weighted average interest rate for the capital leases at December 31, 2018 and 2017 is 3.41% and 3.07%, respectively. Other The Company paid cash for interest of $5.2 million, $4.8 million, and $4.1 million for the years ended December 31, 2018, 2017 and 2016, respectively. The estimated fair value of total debt at December 31, 2018 and 2017 is $122.0 million and $132.3 million, respectively. The carrying amount of debt related to the revolving credit facility approximated fair value as of December 31, 2018 and 2017 due to the existence of variable interest rates, which approximate market rates. The fair value of the capital leases is based on current market interest rates for similar types of financial instruments which reflect Level 2 inputs. Principal Maturities of Long-Term Debt The principal maturities of long-term debt, including interest on capital leases, for the next five years (in thousands) are as follows: Amount 2019 $ 21,311 2020 41,311 2021 21,837 2022 19,947 2023 14,522 Thereafter 14,356 Total 133,284 Less: Amounts Representing Interest on Capital Leases 10,425 Total $ 122,859

Commitments, Contingencies and

Commitments, Contingencies and Uncertainties	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments, Contingencies and Uncertainties	3. Commitments, Contingencies and Uncertainties The Company leases certain service facilities and equipment. Rent expense was $23.2 million, $21.1 million, and $18.1 million for the years ended December 31, 2018, 2017 and 2016, respectively. At December 31, 2018, the Company was committed under non-cancellable operating lease agreements requiring minimum annual rentals payable as follows (in thousands): Amount 2019 $ 21,285 2020 16,978 2021 14,159 2022 11,482 2023 8,215 Thereafter 22,531 Total $ 94,650 Management expects that in the normal course of business, leases will be renewed or replaced as they expire. Capital expenditures committed were $25.6 million at December 31, 2018. As of December 31, 2018 and 2017, the Company had $22.0 million and $11.2 million, respectively, of capital expenditures in accounts payable. Other. The Company pays its pro rata share of the cost of letters of credit outstanding for certain workers’ compensation claims incurred prior to March 1, 2000 that Saia’s former parent maintains for insurance programs. The Company’s pro rata share of these outstanding letters of credit was $1.8 million at December 31, 2018 and 2017. The Company is subject to legal proceedings that arise in the ordinary course of its business. Management believes that adequate provisions for resolution of all contingencies, claims and pending litigation have been made for probable and estimable losses and that the ultimate outcome of these actions will not have a material adverse effect on its financial condition but could have a material adverse effect on its results of operations in a given quarter or annual period.

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	4. Goodwill and Other Intangible Assets The changes in gross carrying amounts of goodwill are as follows (in thousands): Goodwill December 31, 2016 $ 12,105 Goodwill acquired — December 31, 2017 12,105 Goodwill acquired — December 31, 2018 $ 12,105 The Company assesses goodwill for impairment on an annual basis in the fourth quarter, or more frequently if events or changes in circumstances indicate that the asset might be impaired. The Company reviews other intangible assets, including customer relationships and non-compete agreements, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of long-lived assets is measured by a comparison of the carrying amount of the asset group to the future undiscounted net cash flows expected to be generated by those assets. If such assets are considered to be impaired, the impairment charge recognized is the amount by which the carrying amounts of the assets exceeds the fair value of the assets. The gross amounts and accumulated amortization of identifiable intangible assets are as follows (in thousands): December 31, 2018 December 31, 2017 Gross Amount Accumulated Amortization Gross Amount Accumulated Amortization Amortizable intangible assets: Customer relationships (useful life of 6-15 years) $ 19,000 $ 9,566 $ 19,000 $ 8,502 Covenants not-to-compete (useful life of 4-6 years) 4,425 4,408 4,425 4,209 Trademarks (useful life of 15 years) 1,500 392 1,500 292 Total $ 24,925 $ 14,366 $ 24,925 $ 13,003 Amortization expense for intangible assets was $1.4 million, $1.4 million and $1.7 million for 2018, 2017 and 2016, respectively. Estimated amortization expense for the five succeeding years follows (in thousands): Amount 2019 $ 1,180 2020 1,163 2021 1,163 2022 1,008 2023 853

Computation of Earnings Per Sha

Computation of Earnings Per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Computation of Earnings Per Share	5. Computation of Earnings Per Share The calculation of basic earnings per common share and diluted earnings per common share is as follows (in thousands except per share amounts): For The Years Ended December 31, 2018 2017 2016 Numerator: Net income $ 104,981 $ 91,129 $ 48,024 Denominator: Denominator for basic earnings per share–weighted average common shares 25,762 25,518 25,038 Effect of dilutive stock options and restricted stock 160 142 51 Effect of other common stock equivalents 369 426 591 Denominator for diluted earnings per share–adjusted weighted average common shares 26,291 26,086 25,680 Basic Earnings Per Share $ 4.08 $ 3.57 $ 1.92 Diluted Earnings Per Share $ 3.99 $ 3.49 $ 1.87 In 2018 and 2017, options and restricted stock for 45,150 and 61,364 shares of common stock, respectively, were excluded from the calculation of diluted earnings per share because their effect was anti-dilutive.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	6. Stockholders’ Equity Deferred Compensation Trust The Saia Executive Capital Accumulation Plan (the Capital Accumulation Plan) allows plan participants to make an irrevocable election to invest in the Company’s common stock. Upon distribution, the funds invested in the Company’s common stock will be paid out in Company stock rather than cash. The following table summarizes the shares of the Company’s common stock that were purchased and sold by the Company’s Rabbi Trust, which holds the investments for the Capital Accumulation Plan: For The Years Ended December 31, 2018 2017 2016 Shares of common stock purchased 10,390 8,220 11,530 Aggregate purchase price of shares purchased $ 700,234 $ 390,542 $ 291,349 Shares of common stock sold 37,086 4,717 10,694 Aggregate sale price of shares sold $ 2,777,630 $ 271,417 $ 322,928 Since the Capital Accumulation Plan provides for the obligation to be settled only in Company stock, the deferred compensation obligation is classified as an equity instrument with no adjustments to operating results based on changes in fair value. Directors’ Deferred Compensation Under the Company’s Directors’ Deferred Fee Plan, non-employee directors may defer all or a portion of their annual fees and retainers which are otherwise payable. Such deferrals are converted into units equivalent to the value of the Company’s stock. Upon the director’s termination, death or disability, accumulated deferrals are distributed in the form of Company common stock. The Company has 240,000 and 228,423 shares reserved for issuance under the Directors’ Deferred Fee Plan at December 31, 2018 and 2017, respectively. The shares reserved for issuance under the Directors’ Deferred Fee Plan are treated as common stock in computing basic earnings per share.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	7. Stock-Based Compensation Prior to the adoption of FASB ASU 2016-09 in 2017, ASC 718 required the benefits of tax deductions in excess of recognized compensation cost to be reported as a financing cash flow, rather than as an operating cash flow. This requirement reduced net operating cash flows and increased net financing cash flows for 2016. For the year ended December 31, 2016, the associated cash flows from financing activities were $0.5 million. For the years ended December 31, 2018 and 2017, the associated cash flows from operating activities were $0.6 million, and $1.7 million, respectively. The stockholders of the Company approved the 2018 Omnibus Incentive Plan (the 2018 Omnibus Plan), the Second Amended and Restated 2011 Omnibus Incentive Plan (the 2011 Omnibus Plan) and Amended and Restated 2003 Omnibus Incentive Plan (the 2003 Omnibus Plan) to allow the Company to issue equity based compensation to help attract and retain executive, managerial, supervisory or professional employees and non-employee directors. The 2018 Omnibus Plan has 1,100,000 shares of common stock reserved. The 2011 Omnibus Plan had a total of 2,350,000 shares of common stock reserved. Following stockholder approval of the 2018 Omnibus Plan, no additional awards have been made under the 2011 Omnibus Plan. The Company had reserved 1,236,000 shares of its common stock under the 2003 Omnibus Plan. Following stockholder approval of the 2011 Omnibus Plan, no additional grants have been made under the 2003 Omnibus Plan. The 2018 Omnibus Plan, the 2011 Omnibus Plan and the 2003 Omnibus Plan provide for the grant or award of stock options; stock appreciation rights; restricted and unrestricted stock; restricted stock units; and Performance Unit Awards. Stock option awards are granted with an exercise price equal to the market price of the Company’s stock at the date of grant; stock option awards granted to employees under the plans to date are non-qualified stock options, have cliff vesting at the end of three years of continuous service, subject to earlier vesting upon a change of control and certain other events, and have a seven-year contractual term. There are no outstanding stock options held by non-employee directors, and no stock options have been granted to non-employee directors under the 2018 Omnibus Plan or the 2011 Omnibus Plan. The 2011 Omnibus Plan provided for an annual grant to each non-employee director of no more than 12,000 shares with the exact number of shares granted each year determined by the Compensation Committee of the Board. These share awards vest over three years subject to acceleration of vesting upon leaving the Board (other than for cause) or a change in control. Shares issued to each non-employee director under this provision were 1,363, 1,942, and 3,279 for the years ended December 31, 2018, 2017 and 2016, respectively. Non-employee directors were also issued in lieu of cash compensation in the aggregate 11,577, 15,152 and 23,734 units equivalent to shares in the Company’s common stock under the Directors’ Deferred Fee Plan during the years ended December 31, 2018, 2017 and 2016, respectively. At December 31, 2018 and 2017, no shares remain reserved and unissued under the provisions of the 2003 Omnibus Plan. At December 31, 2018 and 2017, 637,695 and 756,218 shares, respectively, remain reserved and unissued under the provisions of the 2011 Omnibus Plan, a portion of which are allocated to outstanding Performance Unit Awards, outstanding stock options and restricted stock described below. At December 31, 2018, 1,100,000 shares remain reserved and unissued under the provisions of the 2018 Omnibus Plan. The Company has historically issued new shares to satisfy stock option exercises or other awards issued under the 2018 Omnibus Plan, 2011 Omnibus Plan and 2003 Omnibus Plan. The years ended December 31, 2018, 2017 and 2016 had stock option and restricted stock compensation expense of $2.1 million, $2.3 million and $2.0 million, respectively, included in salaries, wages and employees’ benefits. The Company recognized a tax benefit consistent with the appropriate tax rates for each of the respective periods. As of December 31, 2018, there is unrecognized compensation expense of $2.8 million related to unvested stock options and restricted stock, which is expected to be recognized over a weighted average period of 1.9 years. The following table summarizes stock option activity for the year ended December 31, 2018 for employees: Options Weighted Average Exercise price Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value (000’s) Outstanding at December 31, 2017 335,000 $ 34.75 Granted 46,500 Exercised (105,860 ) Forfeited (9,330 ) Outstanding at December 31, 2018 266,310 $ 38.93 4.6 $ 5,289 Exercisable at December 31, 2018 8,830 $ 43.01 3.1 $ 113 The total intrinsic value of options exercised during the years ended December 31, 2018, 2017 and 2016 was $3.5 million, $3.5 million, and $2.5 million, respectively. The weighted-average grant-date fair value per share of options granted during the years ended December 31, 2018, 2017 and 2016 was $23.74, $15.49, and $9.99, respectively. The weighted-average grant-date fair value per share of options vested during the years ended December 31, 2018, 2017 and 2016 was $15.41, $12.26, and $12.95, respectively. The following table summarizes the weighted average assumptions used in valuing options for the years ended December 31, 2018, 2017 and 2016: 2018 2017 2016 Risk free interest rate 2.24 % 1.89 % 1.63 % Expected life in years 4.2 4.5 4.5 Expected volatility 36.31 % 36.90 % 41.42 % Dividend rate — — — The risk-free interest rate for periods within the contractual life of the option is based on the U.S. Treasury yield in effect at the time of grant. The expected life of the options represents the period of time that options granted are expected to be outstanding. Expected volatilities are based on historical volatility of the Company’s stock. The following table summarizes the status of the Company’s unvested options as of December 31, 2018 and changes during the year ended December 31, 2018: Options Weighted Average Grant-date Fair Value Unvested at December 31, 2017 309,720 $ 12.38 Granted 46,500 23.74 Vested (89,410 ) 15.41 Forfeited (9,330 ) 13.00 Unvested at December 31, 2018 257,480 $ 13.36 The Company granted shares of restricted stock to certain key executives in February 2013, September 2014, May 2015, February 2016 and August 2017. All of these shares of restricted stock awards vest 25% after three years, 25% after four years and the remaining 50% after five years assuming the executive has been in continuous service to the Company since the award date, subject to earlier vesting upon a change in control. Commencing in 2017, the Company began granting shares of restricted stock as part of its long-term incentive plan. These shares of restricted stock cliff vest in three years, subject to earlier vesting upon a change in control. The value of restricted stock is based on the fair market value of the Company’s common stock at the date of grant. The following table summarizes restricted stock activity during the year ended December 31, 2018: Shares Weighted Average Grant-date Fair Value Restricted Stock at December 31, 2017 57,857 $ 42.10 Granted 16,562 73.35 Vested (2,896 ) 47.46 Forfeited (1,162 ) 57.48 Restricted Stock at December 31, 2018 70,361 $ 48.98 Performance Unit Awards Under the 2011 Omnibus Plan, the Compensation Committee of the Board of Directors approved Performance Unit Awards to a group of less than 20 management and executive employees. The criteria for payout of the awards is based on a comparison over the three-year performance period of these awards of the total shareholder return (TSR) of the Company’s common stock compared to the TSR of the companies in the peer group established by the Compensation Committee. The stock-based awards are accounted for in accordance with ASC 718 with the expense amortized over the three-year vesting period based on the fair value using the Monte Carlo method at the date the awards are granted. Operating results include expense for the Performance Unit Awards of $2.4 million in 2018, $1.9 million in 2017 and $1.6 million in 2016. Shares earned under the Performance Unit Awards are issued in the first quarter of the year following the end of the performance period. There was an issuance of 128,240 shares for the January 2016 - December 2018 performance period in February 2019, 49,188 shares for the January 2015 - December 2017 performance period in February 2018, and 30,893 shares for the January 2014 - December 2016 performance period in February 2017. The issuance of shares related to these awards would range from zero to a maximum of 128,240 shares per year as of December 31, 2018.

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Employee Benefits	8. Employee Benefits Defined Contribution Plans The Company sponsors defined contribution plans. The plans principally consist of contributory 401(k) savings plans and noncontributory profit sharing plans. The Company’s contributions to the 401(k) savings plans consist of a matching percentage. The Company match has historically been 50 percent of the first six percent of an eligible employee’s contributions. The Company’s total contributions to the 401(k) savings plans included in continuing operations for the years ended December 31, 2018, 2017 and 2016, were $9.9 million, $8.3 million, and $7.1 million, respectively. Deferred Compensation Plan The Capital Accumulation Plan is a nonqualified deferred compensation plan for Saia executives. The Capital Accumulation Plan allows for the plan participants to invest in the Company’s common stock. Elections to invest in the Company’s common stock are irrevocable and upon distribution, the funds invested in the Company’s common stock will be paid out in Company common stock rather than cash. At December 31, 2018 and 2017, the Company’s Rabbi Trust, which holds the investments for the Capital Accumulation Plan, held 143,614 and 170,310 shares of the Company’s common stock, respectively, all of which were purchased on the open market. The shares held by the Capital Accumulation Plan are treated similar to treasury shares and deducted from basic shares outstanding for purposes of calculating basic earnings per share. However, because the distributions are required to be made in Company stock, these shares are added back to basic shares outstanding for the purposes of calculating diluted earnings per share. Annual Incentive Awards The Company provides annual cash performance incentive awards to certain salaried employees which are based primarily on actual operating results achieved for the year, compared to targeted operating results. Operating results include performance incentives of $19.9 million, $12.2 million, and $5.1 million in 2018, 2017 and 2016, respectively. Cash performance incentive awards for a year are primarily paid in the first quarter of the following year. Employee Stock Purchase Plan In January 2003, the Company adopted the Employee Stock Purchase Plan of Saia, Inc. (ESPP) allowing all eligible employees to purchase common stock of the Company at current market prices through payroll deductions of up to 10 percent of annual wages. In 2015, the Company amended the ESPP to allow highly compensated employees as defined by Section 401(a)(17) of the Internal Revenue Code to make payroll deductions of up to 20 percent of annual wages. The custodian uses the funds to purchase the Company’s common stock at current market prices. The custodian purchased 6,840, 8,063, and 20,532 shares in the open market during 2018, 2017 and 2016, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The Tax Cuts and Jobs Act The Tax Cuts and Jobs Act (the Act) was enacted on December 22, 2017. The Act reduces the U.S. federal corporate tax rate from 35 percent to 21 percent, allows for immediate deductibility of certain qualified depreciable assets, other changes in the deductibility of items and requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. The Company recognized a tax benefit amount of $34 million to reflect the estimated impact of the Act, which is included as a component of income tax expense in 2017. No material changes to this estimate were recognized in 2018. The 2017 tax benefit is the result of remeasuring certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, generally 21 percent. Other Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Deferred tax liabilities (assets) are comprised of the following at December 31 (in thousands): 2018 2017 Depreciation $ 115,775 $ 86,506 Other 2,977 93 Gross deferred tax liabilities 118,752 86,599 Allowance for doubtful accounts (995 ) (988 ) Equity-based compensation (3,444 ) (2,607 ) Employee benefits (6,139 ) (5,458 ) Claims and insurance (17,176 ) (16,929 ) Other (4,105 ) (1,194 ) Gross deferred tax assets (31,859 ) (27,176 ) Net deferred tax liability $ 86,893 $ 59,423 The Company has determined that a valuation allowance was not necessary at December 31, 2018 or 2017 for substantially all deferred tax assets since it is more likely than not they will be realized from future reversals of temporary differences or future taxable income. The income tax provision (benefit) for continuing operations consists of the following (in thousands): 2018 2017 2016 Current: U.S. federal $ 1,650 $ 17,637 $ 12,127 State 1,732 1,761 1,988 Total current income tax provision 3,382 19,398 14,115 Deferred: U.S. federal 27,114 (21,221 ) 12,599 State 356 445 181 Total deferred income tax provision 27,470 (20,776 ) 12,780 Total income tax provision $ 30,852 $ (1,378 ) $ 26,895 A reconciliation between income taxes at the federal statutory rate (21 or 35 percent) and the effective income tax provision is as follows (in thousands): 2018 2017 2016 Provision at federal statutory rate $ 28,525 $ 31,422 $ 26,222 State income taxes, net 4,468 2,545 2,418 Tax Cuts and Jobs Act benefit — (33,910 ) — Nondeductible business expenses (benefits) (49 ) (913 ) 462 Tax credits (1,659 ) (190 ) (1,278 ) Other, net (433 ) (332 ) (929 ) Total provision $ 30,852 $ (1,378 ) $ 26,895 The Company and its subsidiaries file income tax returns in the U.S. federal jurisdiction and various state jurisdictions. For the U.S. federal jurisdiction, tax years 2015 - 2018 remain open to examination. The expiration of the statute of limitations related to the various state income tax returns that the Company files varies by state. In general, tax years 2009-2018 remain open to examination by the various state and local jurisdictions. However, a state could challenge certain tax positions back to the 2005 tax year. A reconciliation of the beginning and ending total amounts of gross unrecognized tax benefits is as follows (in thousands): 2018 2017 Gross unrecognized tax benefits at beginning of year $ 1,093 $ 1,280 Gross decreases in tax positions for prior years (341 ) (7 ) Gross increases in tax positions for current year 319 171 Settlements — — Lapse of statute of limitations (202 ) (351 ) Gross unrecognized tax benefits at end of year $ 869 $ 1,093 The Company recognizes interest and penalties related to uncertain tax positions as a component of income tax expense. During the years ended December 31, 2018 and 2017, the Company did not record any interest related to unrecognized tax benefits. During the year ended December 31, 2016, the Company recorded interest related to unrecognized tax benefits of approximately $0.1 million. The Company had approximately $0.1 million and $0.1 million of accrued interest and penalties at December 31, 2018 and 2017, respectively. The total amount of unrecognized tax benefits, which is recorded within claims, insurance and other liabilities on the consolidated balance sheets, that would affect the Company’s effective tax rate if recognized is $0.9 million and $1.1 million as of December 31, 2018 and 2017, respectively. The Company paid cash for income taxes of $1.9 million, $17.0 million, and $5.4 million in 2018, 2017 and 2016, respectively. The Company does not anticipate total unrecognized tax benefits will significantly change during the next twelve months due to the settlements of audits and the expiration of statutes of limitations. In 2017, the Company recognized a $34 million benefit related to the impact of the Act described above and a $1.7 million benefit related to excess tax benefits from stock activity recognized as a result of the Company’s adoption of ASU 2016-09 effective January 1, 2017. As a result of legislation enacted in the fourth quarter of 2015, the Company recognized tax credits for alternative fuel usage of approximately $1.0 million in 2016. In February 2018, US federal tax law changes were enacted that reinstated the tax credits for alternative fuel usage for 2017. The Company recognized the tax credits of approximately $1.0 million in 2018.

Summary of Quarterly Operating

Summary of Quarterly Operating Results (unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Operating Results (unaudited)	10. Summary of Quarterly Operating Results (unaudited) (Amounts in thousands, except per share data) Three months ended, 2018 March 31 June 30 September 30 December 31 Operating revenue $ 392,805 $ 428,732 $ 425,562 $ 406,750 Operating income 27,579 41,565 38,697 33,336 Net income 21,125 30,281 28,195 25,380 Basic earnings per share $ 0.82 $ 1.18 $ 1.09 $ 0.98 Diluted earnings per share $ 0.80 $ 1.15 $ 1.07 $ 0.97 Three months ended, 2017 March 31 June 30 September 30 December 31 Operating revenue $ 323,090 $ 364,404 $ 357,010 $ 360,196 Operating income 17,527 29,686 24,568 22,928 Net income 11,395 17,571 14,373 47,789 Basic earnings per share $ 0.45 $ 0.69 $ 0.56 $ 1.87 Diluted earnings per share $ 0.44 $ 0.68 $ 0.55 $ 1.82

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
Valuation And Qualifying Accounts [Abstract]
Valuation and Qualifying Accounts	11. Valuation and Qualifying Accounts For the Years Ended December 31, 2018, 2017 and 2016 (in thousands) Additions Balance, beginning of period Charged to costs and expenses Charged to other accounts Deductions(1) Balance, end of period Year ended December 31, 2018: Deducted from asset account – Allowance for uncollectible accounts $ 3,991 $ 1,978 $ — $ (1,941 ) $ 4,028 Year ended December 31, 2017: Deducted from asset account – Allowance for uncollectible accounts 3,222 2,634 — (1,865 ) 3,991 Year ended December 31, 2016: Deducted from asset account – Allowance for uncollectible accounts 3,451 1,475 — (1,704 ) 3,222 (1) Primarily uncollectible accounts written off — net of recoveries.

Description of Business and S_2

Description of Business and Summary of Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Description of Business	Description of Business Saia, Inc. and its subsidiaries (Saia or the Company) are headquartered in Johns Creek, Georgia. Saia is a leading, less-than-truckload (“LTL”) motor carrier with more than 97% of its revenue historically derived from transporting LTL shipments for customers. In addition to the core LTL services provided in 41 states, the Company also offers customers a wide range of other value-added services, including non-asset truckload, expedited and logistics services across the United States. The Chief Operating Decision Maker is the Chief Executive Officer who manages the business, regularly reviews financial information and allocates resources. The Company has one operating segment.
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of Saia, Inc. and its wholly-owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in the consolidated financial statements.
Use of Estimates	Use of Estimates Management makes estimates and assumptions when preparing the consolidated financial statements in conformity with U.S. generally accepted accounting principles. These estimates and assumptions affect the amounts reported in the consolidated financial statements and footnotes. Actual results could differ from those estimates.
Accounting Pronouncements Adopted in 2018	Accounting Pronouncements Adopted in 2018 In May 2014, the FASB issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers As a result of the adoption of this standard, the Company changed the presentation of its non-asset truckload business from net revenue to gross revenue and changed the method of recognizing that revenue from upon commencement of the services to over the transit time of the freight as it moves from origin to destination. The Company has consistently applied the accounting policies to all periods presented in these condensed consolidated financial statements. The below tables reflect the effect of the adoption of this standard on the previously reported financial data. Condensed Consolidated Balance Sheet impact: As of December 31, 2017 As of December 31, 2016 As adjusted As originally reported Effect of change As adjusted As originally reported Effect of change (in thousands) Accounts receivable $ 170,278 $ 170,610 $ (332 ) $ 134,926 $ 135,083 $ (157 ) Total current assets 203,249 203,581 (332 ) 166,322 166,479 (157 ) Total assets 967,315 967,647 (332 ) 800,213 800,370 (157 ) Accounts payable 57,438 57,717 (279 ) 45,018 45,149 (131 ) Total current liabilities 166,926 167,205 (279 ) 144,813 144,944 (131 ) Retained earnings 339,500 339,553 (53 ) 248,371 248,397 (26 ) Total stockholders’ equity 582,494 582,547 (53 ) 483,052 483,078 (26 ) Total liabilities and stockholders’ equity 967,315 967,647 (332 ) 800,213 800,370 (157 ) Condensed Consolidated Statement of Operations Impact: For the quarter ended December 31, 2017 For the year ended December 31, 2017 As adjusted As originally reported Effect of change As adjusted As originally reported Effect of change (in thousands, except per share data) Operating revenue $ 360,196 $ 353,251 $ 6,945 $ 1,404,703 $ 1,378,510 $ 26,193 Purchased transportation 28,185 21,270 6,915 107,702 81,482 26,220 Total operating expenses 337,268 330,353 6,915 1,309,993 1,283,773 26,220 Operating income 22,928 22,898 30 94,710 94,737 (27 ) Net income 47,789 47,759 30 91,129 91,156 (27 ) Basic Earnings Per Share 1.87 1.87 — 3.57 3.57 — Diluted Earnings Per Share 1.82 1.82 — 3.49 3.49 — For the year ended December 31, 2016 As adjusted As originally reported Effect of change (in thousands, except per share data) Operating revenue $ 1,250,391 $ 1,218,481 $ 31,910 Purchased transportation 88,239 56,329 31,910 Total operating expenses 1,171,255 1,139,345 31,910 Operating income 79,136 79,136 — Net income 48,024 48,024 — Basic Earnings Per Share 1.92 1.92 — Diluted Earnings Per Share 1.87 1.87 — Condensed Consolidated Statement of Cash Flows impact: For the year ended December 31, 2017 For the year ended December 31, 2016 As adjusted As originally reported Effect of change As adjusted As originally reported Effect of change (in thousands) Net income $ 91,129 $ 91,156 $ (27 ) $ 48,024 $ 48,024 $ — Changes in operating assets and liabilities, net (7,143 ) (7,170 ) 27 2,592 2,592 — Net cash provided by operating activities 157,846 157,846 — 146,426 146,426 — Net decrease in cash and cash equivalents 3,181 3,181 — 1,415 1,415 —
Accounting Pronouncements Not Yet Adopted	Accounting Pronouncements Not Yet Adopted In February 2016, the FASB established Topic 842, Leases Land Easement Practical Expedient for Transition to Topic 842 Codification Improvements to Topic 842, Leases Targeted Improvements The new standard is effective for the Company on January 1, 2019, with early adoption permitted. The Company will adopt the new standard on its effective date. A modified retrospective transition approach is required, applying the new standard to all leases existing at the date of initial application. An entity may choose to use either (1) its effective date or (2) the beginning of the earliest comparative period presented in the financial statements as its date of initial application. If an entity chooses the second option, the transition requirements for existing leases also apply to leases entered into between the date of initial application and the effective date. The entity must also recast its comparative period financial statements and provide the disclosures required by the new standard for the comparative periods. The Company will adopt the new standard on January 1, 2019 and use the effective date as its date of initial application. Consequently, financial information will not be updated and the disclosures required under the new standard will not be provided for dates and periods before January 1, 2019. The new standard provides a number of optional practical expedients in transition. The Company intends to elect the ‘package of practical expedients’, which permits it not to reassess under the new standard its prior conclusions about lease identification, lease classification and initial direct costs. The Company does not expect to elect the use-of-hindsight or the practical expedient pertaining to land easements; the latter not being applicable to it. The Company expects that this standard will have a material effect on its consolidated financial statements. While the Company continues to assess all of the effects of adoption, it currently believes the most significant effects relate to (1) the recognition of new ROU assets and lease liabilities on its consolidated balance sheet for its real estate operating leases and (2) providing significant new disclosures about its leasing activities. The Company does not expect a significant change in its leasing activities between now and the first financial statements issued with adoption. On adoption, the Company currently expects to recognize additional operating liabilities of approximately $70 to $80 million, with corresponding ROU assets of the same amount based on the present value of the remaining minimum rental payments for existing operating leases. The new standard also provides practical expedients for an entity’s ongoing accounting. The Company currently intends to elect the short-term lease recognition exemption for all leases that qualify. This means, for those leases that qualify, the Company will not recognize ROU assets or lease liabilities, and this includes not recognizing ROU assets or lease liabilities for existing short-term leases of those assets in transition. The Company also currently intends to elect the practical expedient to not separate lease and non-lease components for all of its leases other than leases of real estate.
Cash and Cash Equivalents and Checks Outstanding	Cash and Cash Equivalents and Checks Outstanding: Cash and cash equivalents in excess of current operating requirements are invested in short-term interest bearing instruments purchased with original maturities of three months or less and are stated at cost, which approximates market. Checks outstanding in excess of cash on deposit are classified in accounts payable on the accompanying consolidated balance sheets and in operating activities in the accompanying consolidated statements of cash flows.
Parts, fuel and operating supplies	Parts, fuel and operating supplies: Parts, fuel and operating supplies are carried at average cost and included in other current assets.
Property and Equipment Including Repairs and Maintenance	Property and Equipment Including Repairs and Maintenance: Property and equipment are carried at cost less accumulated depreciation. Depreciation is computed using the straight-line method based on the following service lives: Years Structures 20 to 25 Tractors 6 to 10 Trailers 10 to 14 Other revenue equipment 7 to 14 Technology equipment and software 3 to 5 Other 3 to 10 At December 31, property and equipment consisted of the following (in thousands): 2018 2017 Land $ 100,157 $ 81,487 Structures 321,283 268,723 Tractors 476,875 398,652 Trailers 354,490 305,540 Other revenue equipment 83,571 77,691 Technology equipment and software 110,954 93,754 Other 74,011 64,147 Total property and equipment, at cost $ 1,521,341 $ 1,289,994 Maintenance and repairs are charged to operations while replacements and improvements that extend the asset’s life are capitalized. The Company’s investment in technology equipment and software consists primarily of systems to support customer service, maintenance and freight management. Depreciation was $100.8 million, $85.7 million and $74.5 million for the years ended December 31, 2018, 2017 and 2016, respectively. Depreciation and amortization expense includes amortization of assets under capital lease. At December 31, 2018, trailers acquired under capital leases had a gross carrying value of $132.5 million and accumulated depreciation of $21.6 million. At December 31, 2017, trailers acquired under capital leases had a gross carrying value of $106.3 million and accumulated depreciation of $13.3 million.
Computer Software Developed or Obtained for Internal Use	Computer Software Developed or Obtained for Internal Use: The Company capitalizes certain costs associated with developing or obtaining internal-use software. Capitalizable costs include external direct costs of materials and services utilized in developing or obtaining the software and payroll and payroll-related costs for employees directly associated with the development of the project. For the years ended December 31, 2018, 2017, and 2016, the Company capitalized $1.1 million, $2.1 million, and $1.6 million, respectively, of primarily payroll-related costs.
Claims and Insurance Accruals	Claims and Insurance Accruals: Claims and insurance accruals, both current and long-term, reflect the estimated cost of claims for workers’ compensation (discounted to present value), cargo loss and damage, and bodily injury and property damage not covered by insurance. These costs are included in claims and insurance expense, except for workers’ compensation, which is included in employees’ benefits expense. The liabilities are included in claims and insurance reserves based on estimates of claims incurred. Liabilities for unsettled claims and claims incurred but not yet reported are actuarially determined with respect to workers’ compensation claims and with respect to all other liabilities, estimated based on management’s evaluation of the nature and severity of individual claims and past experience. For workers’ compensation, the amount of the discount at December 31, 2018 and December 31, 2017 was $5.0 million and $3.5 million, respectively. Risk retention amounts per occurrence during the three years ended December 31, 2018, were as follows: Workers’ compensation $ 1,000,000 Bodily injury and property damage 2,000,000 Employee medical and hospitalization 400,000 Cargo loss and damage 250,000 Effective March 1, 2018, the Company entered into a new auto liability policy with a three-year term. The risk retention amount per occurrence remains at $2.0 million under the new policy. The policy includes a limit for a single loss of $8.0 million, an aggregate loss limit of $24.0 million for each policy year, and a $48.0 million aggregate loss limit for the 36-month term ended March 1, 2021. The policy includes a returnable premium of up to $5.2 million, to be adjusted by the insurer for changes in claims, and a provision to extend the term of the policy for one additional 12-month period, if management and the insurer mutually agree to commute the policy for the first 12 months of the policy term. A decision with respect to commutation of the first 12 months of the policy cannot be made before March 1, 2019. The policy also includes a returnable premium of up to $15.6 million, to be adjusted by the insurer for changes in claims, if management and the insurer mutually agree to commute the policy for the entire 36 months. A decision with respect to commutation of the entire policy cannot be made before August 30, 2021, unless both the Company and the insurance carrier agree to a commutation prior to the end of the policy term. Additionally, the Company may be required to pay an additional premium of up to $11.0 million if paid losses are greater than $15.6 million over the three-year policy period. Based on 2018 claims experience, no such additional premium was accrued at December 31, 2018. As of December 31, 2018, no portion of the policy was eligible for commutation, and insufficient claims experience is available to determine the likelihood of future commutations. As such, no related amounts have been recorded at December 31, 2018.
Income Taxes	Income Taxes: Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. As required by FASB Accounting Standards Codification (“ASC”) 740, , the Company follows this guidance which defines the threshold for recognizing the benefits of tax-filing positions in the financial statements as “more-likely-than-not” to be sustained by the tax authority. ASC 740 also prescribes a method for computing the tax benefit of such tax positions to be recognized in the financial statements. In addition, it provides guidance on derecognition, classification, interest and penalties, accounting in interim periods, disclosure and transition.
Revenue Recognition	Revenue Recognition: The Company’s revenues are derived primarily from the transportation of freight as it satisfies performance obligations that arise from contracts with its customers. The Company’s performance obligations arise when it receives a bill of lading (“BOL”) to transport a customer's commodities at negotiated prices contained in either a transportation services agreement or a publicly disclosed tariff rate. Once a BOL is received, a legally-enforceable contract is formed whereby the parties are committed to perform and the rights of the parties, shipping terms and conditions, and payment terms have been identified. A customer may submit many BOLs for transportation services at various times throughout a service agreement term but each shipment represents a distinct service that is a separately identified performance obligation. The average transit time to complete a shipment is between 1 to 5 days. Payments for transportation services are normally billed after completion of the service and are generally due within 30 days after the invoice date. The Company recognizes revenue related to the Company’s LTL, non-asset truckload and expedited services over the transit time of the shipment as it moves from origin to destination. Revenue for services started but not completed at the reporting date is allocated based on the relative transit time in each reporting period, with the portion allocated for services subsequent to the reporting date considered remaining performance obligations. Key estimates included in the recognition and measurement of revenue and related accounts receivable are as follows: • Revenue associated with shipments in transit is recognized ratably over transit time and is based on average cycle times to move shipments from their origin to their final destination or interchange; and • Adjustments to revenue for billing adjustments and collectability. Revenue related to interline transportation services that involve the services of another party, such as another LTL service provider, is reported on a net basis. The portion of the gross amount billed to customers that is remitted by the Company to another party is not reflected as revenue. Revenue from logistics services is recognized as the services are provided. Remaining performance obligations represent the transaction price allocated to future reporting periods for freight services started but not completed at the reporting date. This includes the unearned portion of billed and unbilled amounts for cancellable freight shipments in transit that the Company expects to recognize as revenue in the period subsequent to the reporting date, which is on average less than one week. The Company has elected to apply the optional exemption in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (ASC) 606 as it pertains to additional quantitative disclosures pertaining to remaining performance obligations.
Stock-Based Compensation	Stock-Based Compensation: The Company accounts for its employee stock-based compensation awards in accordance with ASC 718, . ASC 718 requires that all employee stock-based compensation is recognized as an expense in the financial statements and that for equity-classified awards such expenses are measured at the grant date fair value of the award. Stock options are accounted for in accordance with ASC 718 with the expense amortized over the three-year vesting period using a Black-Scholes-Merton model to estimate the fair value of stock options granted to employees. Restricted stock is accounted for in accordance with ASC 718 with the expense amortized over a three to five year vesting period using the intrinsic valuation method to estimate the fair value of restricted stock awards granted to employees. Stock-based Performance Unit Awards are accounted for in accordance with ASC 718 with the expense amortized over the three-year vesting period using a Monte Carlo model to estimate fair value at the date the awards are granted.
Credit Risk	Credit Risk: The Company routinely grants credit to its customers. The risk of significant loss in trade receivables is substantially mitigated by the Company’s credit evaluation process, short collection terms, low revenue per transaction and services performed for a large number of customers with no single customer representing more than 5.0 percent of consolidated operating revenue. Allowances for potential credit losses are based on historical loss experience, current economic environment, expected trends and customer specific factors.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets: As required by ASC 360, , long-lived assets, such as property, plant and equipment, and purchased intangible assets subject to amortization, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If circumstances require a long-lived asset or asset group be tested for possible impairment, the Company first compares undiscounted cash flows expected to be generated by that asset or asset group to its carrying value. If the carrying value of the long-lived asset or asset group is not recoverable on an undiscounted cash flow basis, impairment is recognized to the extent that the carrying value exceeds its fair value. Fair value is determined through various valuation techniques including discounted cash flow models, quoted market values and third-party independent appraisals, as deemed necessary. The Company has adopted ASU 2011-08, Testing Goodwill for Impairment Intangibles – Goodwill and Other
Advertising	Advertising: The costs of advertising are expensed as incurred. Advertising costs charged to expense were $3.9 million, $2.2 million, and $1.2 million in 2018, 2017 and 2016, respectively.
Financial Instruments	Financial Instruments The carrying amounts of financial instruments including cash and cash equivalents, accounts receivable, accounts payable and short-term debt approximated fair value as of December 31, 2018 and 2017, because of the relatively short maturity of these instruments. See Note 2 for fair value disclosures related to long-term debt.

Description of Business and S_3

Description of Business and Summary of Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Summary of Property and Equipment, Estimated Useful Lives	Depreciation is computed using the straight-line method based on the following service lives: Years Structures 20 to 25 Tractors 6 to 10 Trailers 10 to 14 Other revenue equipment 7 to 14 Technology equipment and software 3 to 5 Other 3 to 10
Schedule of Property and Equipment	At December 31, property and equipment consisted of the following (in thousands): 2018 2017 Land $ 100,157 $ 81,487 Structures 321,283 268,723 Tractors 476,875 398,652 Trailers 354,490 305,540 Other revenue equipment 83,571 77,691 Technology equipment and software 110,954 93,754 Other 74,011 64,147 Total property and equipment, at cost $ 1,521,341 $ 1,289,994
Summary of Risk Retention Amounts Per Occurrence	Risk retention amounts per occurrence during the three years ended December 31, 2018, were as follows: Workers’ compensation $ 1,000,000 Bodily injury and property damage 2,000,000 Employee medical and hospitalization 400,000 Cargo loss and damage 250,000
Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers
Effect of Adoption of Standard on Previously Reported Financial Data	The below tables reflect the effect of the adoption of this standard on the previously reported financial data. Condensed Consolidated Balance Sheet impact: As of December 31, 2017 As of December 31, 2016 As adjusted As originally reported Effect of change As adjusted As originally reported Effect of change (in thousands) Accounts receivable $ 170,278 $ 170,610 $ (332 ) $ 134,926 $ 135,083 $ (157 ) Total current assets 203,249 203,581 (332 ) 166,322 166,479 (157 ) Total assets 967,315 967,647 (332 ) 800,213 800,370 (157 ) Accounts payable 57,438 57,717 (279 ) 45,018 45,149 (131 ) Total current liabilities 166,926 167,205 (279 ) 144,813 144,944 (131 ) Retained earnings 339,500 339,553 (53 ) 248,371 248,397 (26 ) Total stockholders’ equity 582,494 582,547 (53 ) 483,052 483,078 (26 ) Total liabilities and stockholders’ equity 967,315 967,647 (332 ) 800,213 800,370 (157 ) Condensed Consolidated Statement of Operations Impact: For the quarter ended December 31, 2017 For the year ended December 31, 2017 As adjusted As originally reported Effect of change As adjusted As originally reported Effect of change (in thousands, except per share data) Operating revenue $ 360,196 $ 353,251 $ 6,945 $ 1,404,703 $ 1,378,510 $ 26,193 Purchased transportation 28,185 21,270 6,915 107,702 81,482 26,220 Total operating expenses 337,268 330,353 6,915 1,309,993 1,283,773 26,220 Operating income 22,928 22,898 30 94,710 94,737 (27 ) Net income 47,789 47,759 30 91,129 91,156 (27 ) Basic Earnings Per Share 1.87 1.87 — 3.57 3.57 — Diluted Earnings Per Share 1.82 1.82 — 3.49 3.49 — For the year ended December 31, 2016 As adjusted As originally reported Effect of change (in thousands, except per share data) Operating revenue $ 1,250,391 $ 1,218,481 $ 31,910 Purchased transportation 88,239 56,329 31,910 Total operating expenses 1,171,255 1,139,345 31,910 Operating income 79,136 79,136 — Net income 48,024 48,024 — Basic Earnings Per Share 1.92 1.92 — Diluted Earnings Per Share 1.87 1.87 — Condensed Consolidated Statement of Cash Flows impact: For the year ended December 31, 2017 For the year ended December 31, 2016 As adjusted As originally reported Effect of change As adjusted As originally reported Effect of change (in thousands) Net income $ 91,129 $ 91,156 $ (27 ) $ 48,024 $ 48,024 $ — Changes in operating assets and liabilities, net (7,143 ) (7,170 ) 27 2,592 2,592 — Net cash provided by operating activities 157,846 157,846 — 146,426 146,426 — Net decrease in cash and cash equivalents 3,181 3,181 — 1,415 1,415 —

Debt and Financing Arrangemen_2

Debt and Financing Arrangements (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Summary of Reconciliation of Debt	At December 31, debt consisted of the following (in thousands): December 31, 2018 December 31, 2017 Credit Agreement with Banks, described below $ 20,000 $ 43,000 Capital Leases, described below 102,859 89,916 Total debt 122,859 132,916 Less: current portion of long-term debt 18,082 14,083 Long-term debt, less current portion $ 104,777 $ 118,833
Schedule of Principal Maturities of Long-Term Debt Including Interest On Capital Leases	The principal maturities of long-term debt, including interest on capital leases, for the next five years (in thousands) are as follows: Amount 2019 $ 21,311 2020 41,311 2021 21,837 2022 19,947 2023 14,522 Thereafter 14,356 Total 133,284 Less: Amounts Representing Interest on Capital Leases 10,425 Total $ 122,859

Commitments, Contingencies an_2

Commitments, Contingencies and Uncertainties (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Schedule of Non-Cancellable Capital And Operating Lease Agreements Requiring Minimum Annual Rentals Payable	At December 31, 2018, the Company was committed under non-cancellable operating lease agreements requiring minimum annual rentals payable as follows (in thousands): Amount 2019 $ 21,285 2020 16,978 2021 14,159 2022 11,482 2023 8,215 Thereafter 22,531 Total $ 94,650

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Summary of Changes in Gross Carrying Amounts of Goodwill	The changes in gross carrying amounts of goodwill are as follows (in thousands): Goodwill December 31, 2016 $ 12,105 Goodwill acquired — December 31, 2017 12,105 Goodwill acquired — December 31, 2018 $ 12,105
Summary of Gross Amounts and Accumulated Amortization of Identifiable Intangible Assets	The gross amounts and accumulated amortization of identifiable intangible assets are as follows (in thousands): December 31, 2018 December 31, 2017 Gross Amount Accumulated Amortization Gross Amount Accumulated Amortization Amortizable intangible assets: Customer relationships (useful life of 6-15 years) $ 19,000 $ 9,566 $ 19,000 $ 8,502 Covenants not-to-compete (useful life of 4-6 years) 4,425 4,408 4,425 4,209 Trademarks (useful life of 15 years) 1,500 392 1,500 292 Total $ 24,925 $ 14,366 $ 24,925 $ 13,003
Summary of Estimated Amortization Expense	Estimated amortization expense for the five succeeding years follows (in thousands): Amount 2019 $ 1,180 2020 1,163 2021 1,163 2022 1,008 2023 853

Computation of Earnings Per S_2

Computation of Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Summary of Calculation of Basic Earnings Per Common Share and Diluted Earnings Per Common Share	The calculation of basic earnings per common share and diluted earnings per common share is as follows (in thousands except per share amounts): For The Years Ended December 31, 2018 2017 2016 Numerator: Net income $ 104,981 $ 91,129 $ 48,024 Denominator: Denominator for basic earnings per share–weighted average common shares 25,762 25,518 25,038 Effect of dilutive stock options and restricted stock 160 142 51 Effect of other common stock equivalents 369 426 591 Denominator for diluted earnings per share–adjusted weighted average common shares 26,291 26,086 25,680 Basic Earnings Per Share $ 4.08 $ 3.57 $ 1.92 Diluted Earnings Per Share $ 3.99 $ 3.49 $ 1.87

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Summary of Purchase and Sale of Common Stock	The following table summarizes the shares of the Company’s common stock that were purchased and sold by the Company’s Rabbi Trust, which holds the investments for the Capital Accumulation Plan: For The Years Ended December 31, 2018 2017 2016 Shares of common stock purchased 10,390 8,220 11,530 Aggregate purchase price of shares purchased $ 700,234 $ 390,542 $ 291,349 Shares of common stock sold 37,086 4,717 10,694 Aggregate sale price of shares sold $ 2,777,630 $ 271,417 $ 322,928

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity	The following table summarizes stock option activity for the year ended December 31, 2018 for employees: Options Weighted Average Exercise price Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value (000’s) Outstanding at December 31, 2017 335,000 $ 34.75 Granted 46,500 Exercised (105,860 ) Forfeited (9,330 ) Outstanding at December 31, 2018 266,310 $ 38.93 4.6 $ 5,289 Exercisable at December 31, 2018 8,830 $ 43.01 3.1 $ 113
Summary of Weighted Average Assumptions Used In Valuing Options	The following table summarizes the weighted average assumptions used in valuing options for the years ended December 31, 2018, 2017 and 2016: 2018 2017 2016 Risk free interest rate 2.24 % 1.89 % 1.63 % Expected life in years 4.2 4.5 4.5 Expected volatility 36.31 % 36.90 % 41.42 % Dividend rate — — —
Summary of Unvested Option	The following table summarizes the status of the Company’s unvested options as of December 31, 2018 and changes during the year ended December 31, 2018: Options Weighted Average Grant-date Fair Value Unvested at December 31, 2017 309,720 $ 12.38 Granted 46,500 23.74 Vested (89,410 ) 15.41 Forfeited (9,330 ) 13.00 Unvested at December 31, 2018 257,480 $ 13.36
Summary of Restricted Stock Activity	The following table summarizes restricted stock activity during the year ended December 31, 2018: Shares Weighted Average Grant-date Fair Value Restricted Stock at December 31, 2017 57,857 $ 42.10 Granted 16,562 73.35 Vested (2,896 ) 47.46 Forfeited (1,162 ) 57.48 Restricted Stock at December 31, 2018 70,361 $ 48.98

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Summary of Deferred Tax Liabilities and Assets	Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Deferred tax liabilities (assets) are comprised of the following at December 31 (in thousands): 2018 2017 Depreciation $ 115,775 $ 86,506 Other 2,977 93 Gross deferred tax liabilities 118,752 86,599 Allowance for doubtful accounts (995 ) (988 ) Equity-based compensation (3,444 ) (2,607 ) Employee benefits (6,139 ) (5,458 ) Claims and insurance (17,176 ) (16,929 ) Other (4,105 ) (1,194 ) Gross deferred tax assets (31,859 ) (27,176 ) Net deferred tax liability $ 86,893 $ 59,423
Summary of Income Tax Provision (Benefit)	The income tax provision (benefit) for continuing operations consists of the following (in thousands): 2018 2017 2016 Current: U.S. federal $ 1,650 $ 17,637 $ 12,127 State 1,732 1,761 1,988 Total current income tax provision 3,382 19,398 14,115 Deferred: U.S. federal 27,114 (21,221 ) 12,599 State 356 445 181 Total deferred income tax provision 27,470 (20,776 ) 12,780 Total income tax provision $ 30,852 $ (1,378 ) $ 26,895
Summary of Reconciliation Between Income Taxes and Effective Income Tax Provision	A reconciliation between income taxes at the federal statutory rate (21 or 35 percent) and the effective income tax provision is as follows (in thousands): 2018 2017 2016 Provision at federal statutory rate $ 28,525 $ 31,422 $ 26,222 State income taxes, net 4,468 2,545 2,418 Tax Cuts and Jobs Act benefit — (33,910 ) — Nondeductible business expenses (benefits) (49 ) (913 ) 462 Tax credits (1,659 ) (190 ) (1,278 ) Other, net (433 ) (332 ) (929 ) Total provision $ 30,852 $ (1,378 ) $ 26,895
Summary of Gross Unrecognized Tax Benefits	A reconciliation of the beginning and ending total amounts of gross unrecognized tax benefits is as follows (in thousands): 2018 2017 Gross unrecognized tax benefits at beginning of year $ 1,093 $ 1,280 Gross decreases in tax positions for prior years (341 ) (7 ) Gross increases in tax positions for current year 319 171 Settlements — — Lapse of statute of limitations (202 ) (351 ) Gross unrecognized tax benefits at end of year $ 869 $ 1,093

Summary of Quarterly Operatin_2

Summary of Quarterly Operating Results (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Operating Results (Unaudited)	(Amounts in thousands, except per share data) Three months ended, 2018 March 31 June 30 September 30 December 31 Operating revenue $ 392,805 $ 428,732 $ 425,562 $ 406,750 Operating income 27,579 41,565 38,697 33,336 Net income 21,125 30,281 28,195 25,380 Basic earnings per share $ 0.82 $ 1.18 $ 1.09 $ 0.98 Diluted earnings per share $ 0.80 $ 1.15 $ 1.07 $ 0.97 Three months ended, 2017 March 31 June 30 September 30 December 31 Operating revenue $ 323,090 $ 364,404 $ 357,010 $ 360,196 Operating income 17,527 29,686 24,568 22,928 Net income 11,395 17,571 14,373 47,789 Basic earnings per share $ 0.45 $ 0.69 $ 0.56 $ 1.87 Diluted earnings per share $ 0.44 $ 0.68 $ 0.55 $ 1.82

Valuation and Qualifying Acco_2

Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2018
Valuation And Qualifying Accounts [Abstract]
Summary of Valuation and Qualifying Accounts	For the Years Ended December 31, 2018, 2017 and 2016 (in thousands) Additions Balance, beginning of period Charged to costs and expenses Charged to other accounts Deductions(1) Balance, end of period Year ended December 31, 2018: Deducted from asset account – Allowance for uncollectible accounts $ 3,991 $ 1,978 $ — $ (1,941 ) $ 4,028 Year ended December 31, 2017: Deducted from asset account – Allowance for uncollectible accounts 3,222 2,634 — (1,865 ) 3,991 Year ended December 31, 2016: Deducted from asset account – Allowance for uncollectible accounts 3,451 1,475 — (1,704 ) 3,222 (1) Primarily uncollectible accounts written off — net of recoveries.

Description of Business and S_4

Description of Business and Summary of Accounting Policies - Additional Information (Detail)	Mar. 01, 2018USD ($)	Dec. 31, 2018USD ($)SegmentCustomer	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Description of Business and Summary of Significant Accounting Policies [Line Items]
Number of operating segments | Segment		1
Depreciation		$ 100,800,000	$ 85,700,000	$ 74,500,000
Primary payroll-related costs capitalized		1,100,000	2,100,000	1,600,000
Workers' compensation discount, amount		$ 5,000,000	3,500,000
Stock-based awards compensation expense amortization period		3 years
Advertising costs		$ 3,900,000	2,200,000	$ 1,200,000
Product Concentration Risk [Member] | Sales Revenue, Net [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Number of customers | Customer		0
Percentage of consolidated operating revenue		5.00%
Restricted Stock [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Stock-based awards compensation expense amortization period		3 years
New Auto Liability Policy [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
New auto liability policy, effective date	Mar. 1, 2018
New auto liability policy, term	3 years
Risk retention amount per occurrence remains under new policy	$ 2,000,000
Provisional extended term of policy	12 months
Accrued additional premium		$ 0
Policy description		Effective March 1, 2018, the Company entered into a new auto liability policy with a three-year term. The risk retention amount per occurrence remains at $2.0 million under the new policy. The policy includes a limit for a single loss of $8.0 million, an aggregate loss limit of $24.0 million for each policy year, and a $48.0 million aggregate loss limit for the 36-month term ended March 1, 2021. The policy includes a returnable premium of up to $5.2 million, to be adjusted by the insurer for changes in claims, and a provision to extend the term of the policy for one additional 12-month period, if management and the insurer mutually agree to commute the policy for the first 12 months of the policy term. A decision with respect to commutation of the first 12 months of the policy cannot be made before March 1, 2019. The policy also includes a returnable premium of up to $15.6 million, to be adjusted by the insurer for changes in claims, if management and the insurer mutually agree to commute the policy for the entire 36 months. A decision with respect to commutation of the entire policy cannot be made before August 30, 2021, unless both the Company and the insurance carrier agree to a commutation prior to the end of the policy term. Additionally, the Company may be required to pay an additional premium of up to $11.0 million if paid losses are greater than $15.6 million over the three-year policy period.
Trailers [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Assets acquired under capital lease, gross		$ 132,500,000	106,300,000
Assets acquired under capital lease, accumulated depreciation		$ 21,600,000	$ 13,300,000
Minimum [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Percentage of revenue derived from transporting		97.00%
Average transit time		1 day
Minimum [Member] | Restricted Stock [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Stock-based awards compensation expense amortization period		3 years
Minimum [Member] | New Auto Liability Policy [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Paid losses specified limit to pay additional premium	$ 15,600,000
Minimum [Member] | ASU No. 2016-02 [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Expected additional operating liabilities to be recognized		$ 70,000,000
Maximum [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Average transit time		5 days
Maximum [Member] | Restricted Stock [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Stock-based awards compensation expense amortization period		5 years
Maximum [Member] | New Auto Liability Policy [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Single loss limit	8,000,000
Aggregate loss limit for each policy year	24,000,000
Aggregate loss limit during policy period	48,000,000
Additional premium to be paid, if paid losses are greater than limit specified	11,000,000
Maximum [Member] | New Auto Liability Policy [Member] | First 12 months [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Returnable premium for changes in claims	5,200,000
Maximum [Member] | New Auto Liability Policy [Member] | Entire 36 Months [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Returnable premium for changes in claims	$ 15,600,000
Maximum [Member] | ASU No. 2016-02 [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Expected additional operating liabilities to be recognized		$ 80,000,000

Description of Business and S_5

Description of Business and Summary of Accounting Policies - Effect of Adoption of Standard on Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable	$ 181,612	$ 170,278	$ 134,926
Total current assets	213,373	203,249	166,322
Total assets	1,133,743	967,315	800,213
Accounts payable	78,994	57,438	45,018
Total current liabilities	209,310	166,926	144,813
Retained earnings	444,481	339,500	248,371
Total stockholders’ equity	695,864	582,494	483,052	$ 427,863
Total liabilities and stockholders’ equity	$ 1,133,743	967,315	800,213
Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers | As Originally Reported
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable		170,610	135,083
Total current assets		203,581	166,479
Total assets		967,647	800,370
Accounts payable		57,717	45,149
Total current liabilities		167,205	144,944
Retained earnings		339,553	248,397
Total stockholders’ equity		582,547	483,078
Total liabilities and stockholders’ equity		967,647	800,370
Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers | Effect of Change
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable		(332)	(157)
Total current assets		(332)	(157)
Total assets		(332)	(157)
Accounts payable		(279)	(131)
Total current liabilities		(279)	(131)
Retained earnings		(53)	(26)
Total stockholders’ equity		(53)	(26)
Total liabilities and stockholders’ equity		$ (332)	$ (157)

Description of Business and S_6

Description of Business and Summary of Accounting Policies - Effect of Adoption of Standard on Condensed Consolidated Statement of Operations (Detail) - 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
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenue	$ 406,750	$ 425,562	$ 428,732	$ 392,805	$ 360,196	$ 357,010	$ 364,404	$ 323,090	$ 1,653,849	$ 1,404,703	$ 1,250,391
Purchased transportation					28,185				123,904	107,702	88,239
Total operating expenses					337,268					1,309,993	1,171,255
Operating income	33,336	38,697	41,565	27,579	22,928	24,568	29,686	17,527	141,177	94,710	79,136
Net income	$ 25,380	$ 28,195	$ 30,281	$ 21,125	$ 47,789	$ 14,373	$ 17,571	$ 11,395	$ 104,981	$ 91,129	$ 48,024
Basic Earnings Per Share	$ 0.98	$ 1.09	$ 1.18	$ 0.82	$ 1.87	$ 0.56	$ 0.69	$ 0.45	$ 4.08	$ 3.57	$ 1.92
Diluted Earnings Per Share	$ 0.97	$ 1.07	$ 1.15	$ 0.80	$ 1.82	$ 0.55	$ 0.68	$ 0.44	$ 3.99	$ 3.49	$ 1.87
Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers | As Originally Reported
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenue					$ 353,251					$ 1,378,510	$ 1,218,481
Purchased transportation					21,270					81,482	56,329
Total operating expenses					330,353					1,283,773	1,139,345
Operating income					22,898					94,737	79,136
Net income					$ 47,759					$ 91,156	$ 48,024
Basic Earnings Per Share					$ 1.87					$ 3.57	$ 1.92
Diluted Earnings Per Share					$ 1.82					$ 3.49	$ 1.87
Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers | Effect of Change
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenue					$ 6,945					$ 26,193	$ 31,910
Purchased transportation					6,915					26,220	31,910
Total operating expenses					6,915					26,220	$ 31,910
Operating income					30					(27)
Net income					$ 30					$ (27)

Description of Business and S_7

Description of Business and Summary of Accounting Policies - Effect of Adoption of Standard on Condensed Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net income	$ 104,981	$ 91,129	$ 48,024
Changes in operating assets and liabilities, net		(7,143)	2,592
Net cash provided by operating activities		157,846	146,426
Net decrease in cash and cash equivalents	$ (2,526)	3,181	1,415
Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers | As Originally Reported
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net income		91,156	48,024
Changes in operating assets and liabilities, net		(7,170)	2,592
Net cash provided by operating activities		157,846	146,426
Net decrease in cash and cash equivalents		3,181	$ 1,415
Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers | Effect of Change
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net income		(27)
Changes in operating assets and liabilities, net		$ 27

Description of Business and S_8

Description of Business and Summary of Accounting Policies - Summary of Property and Equipment, Estimated Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2018
Structures [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	20 years
Structures [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	25 years
Tractors [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	6 years
Tractors [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	10 years
Trailers [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	10 years
Trailers [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	14 years
Other Revenue Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	7 years
Other Revenue Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	14 years
Technology Equipment and Software [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	3 years
Technology Equipment and Software [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	5 years
Other [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	3 years
Other [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, service lives	10 years

Description of Business and S_9

Description of Business and Summary of Accounting Policies - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 1,521,341	$ 1,289,994
Land [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	100,157	81,487
Structures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	321,283	268,723
Tractors [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	476,875	398,652
Trailers [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	354,490	305,540
Other Revenue Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	83,571	77,691
Technology Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	110,954	93,754
Other [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 74,011	$ 64,147

Description of Business and _10

Description of Business and Summary of Accounting Policies - Summary of Risk Retention Amounts Per Occurrence (Detail)	36 Months Ended
	Dec. 31, 2018USD ($)
Schedule Of Retention Amounts For Uninsured Claims Per Occurrence Basis [Abstract]
Workers’ compensation	$ 1,000,000
Bodily injury and property damage	2,000,000
Employee medical and hospitalization	400,000
Cargo loss and damage	$ 250,000

Description of Business and _11

Description of Business and Summary of Accounting Policies - Additional Information1 (Detail)	Dec. 31, 2018
Maximum [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Description of Business and Summary of Significant Accounting Policies [Line Items]
Payment terms	30 days

Debt and Financing Arrangemen_3

Debt and Financing Arrangements - Summary of Reconciliation of Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Capital Leases, described below	$ 102,859	$ 89,916
Total debt	122,859	132,916
Less: current portion of long-term debt	18,082	14,083
Long-term debt, less current portion	104,777	118,833
Existing Credit Agreement [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit Agreement with Banks, described below	$ 20,000	$ 43,000

Debt and Financing Arrangemen_4

Debt and Financing Arrangements - Additional Information (Detail) - USD ($)	Feb. 05, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 04, 2019
Debt Instrument [Line Items]
Letter of credit facility outstanding amount		$ 1,800,000	$ 1,800,000
Capital Leases, described below		$ 102,859,000	89,916,000
Lease expiration period		7 years
Cash paid for interest		$ 5,200,000	4,800,000	$ 4,100,000
Estimated fair value of total debt		$ 122,000,000	$ 132,300,000
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Weighted average interest rate for capital lease		3.41%	3.07%
Existing Credit Agreement [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Amendment line of credit facility expiration year and month		2020-03
Additional borrowing capacity under revolving credit facility		$ 75,000,000
Credit Agreement with Banks		20,000,000	$ 43,000,000
Letter of credit facility outstanding amount		27,700,000	$ 33,900,000
Existing Credit Agreement [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowing capacity under credit agreement		$ 250,000,000
Rate margin		2.25%
Letter of credit unused portion fee		0.30%
Existing Credit Agreement [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Rate margin		1.125%
Letter of credit unused portion fee		0.20%
Existing Credit Agreement [Member] | LIBOR Rate Margin [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Rate margin		2.25%
Existing Credit Agreement [Member] | LIBOR Rate Margin [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Rate margin		1.125%
Existing Credit Agreement [Member] | Base Rate Margin [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Rate margin		0.50%
Existing Credit Agreement [Member] | Base Rate Margin [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Rate margin		0.125%
Credit Agreement [Member] | Revolving Credit Facility [Member] | Credit Agreement Before Amendments | Subsequent Event [Member]
Debt Instrument [Line Items]
Borrowing capacity under credit agreement					$ 250,000,000
Restated Credit Agreement [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Amendment line of credit facility expiration year and month	2024-02
Restated Credit Agreement [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Borrowing capacity under credit agreement	$ 300,000,000
Additional borrowing capacity under revolving credit facility	$ 100,000,000
Minimum debt service coverage ratio	125.00%
Maximum leverage ratio	325.00%
Restated Credit Agreement [Member] | Maximum [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Rate margin	2.00%
Letter of credit unused portion fee	0.30%
Restated Credit Agreement [Member] | Minimum [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Rate margin	1.00%
Letter of credit unused portion fee	0.175%
Restated Credit Agreement [Member] | LIBOR Rate Margin [Member] | Maximum [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Rate margin	2.00%
Restated Credit Agreement [Member] | LIBOR Rate Margin [Member] | Minimum [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Rate margin	1.00%
Restated Credit Agreement [Member] | Base Rate Margin [Member] | Maximum [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Rate margin	0.50%
Restated Credit Agreement [Member] | Base Rate Margin [Member] | Minimum [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Rate margin	0.50%

Debt and Financing Arrangemen_5

Debt and Financing Arrangements - Schedule of Principal Maturities of Long-Term Debt Including Interest On Capital Leases (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
2,019	$ 21,311
2,020	41,311
2,021	21,837
2,022	19,947
2,023	14,522
Thereafter	14,356
Total	133,284
Total	122,859	$ 132,916
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Less: Amounts Representing Interest on Capital Leases	$ 10,425

Commitments, Contingencies an_3

Commitments, Contingencies and Uncertainties - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Rent expense	$ 23.2	$ 21.1	$ 18.1
Capital expenditures committed	25.6
Capital expenditures in accounts payable	22	11.2
Pro rata share of letters of credit outstanding	$ 1.8	$ 1.8

Commitments, Contingencies an_4

Commitments, Contingencies and Uncertainties - Schedule of Non-Cancellable Capital and Operating Lease Agreements Requiring Minimum Annual Rentals Payable (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,019	$ 21,285
2,020	16,978
2,021	14,159
2,022	11,482
2,023	8,215
Thereafter	22,531
Total	$ 94,650

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Summary of Changes in Gross Carrying Amounts of Goodwill (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Goodwill Roll Forward
Goodwill, Beginning Balance	$ 12,105	$ 12,105
Goodwill, Ending Balance	$ 12,105	$ 12,105

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Summary of Gross Amounts and Accumulated Amortization of Identifiable Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 24,925	$ 24,925
Accumulated Amortization	14,366	13,003
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Amount	19,000	19,000
Accumulated Amortization	9,566	8,502
Covenants not-to-Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Amount	4,425	4,425
Accumulated Amortization	4,408	4,209
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Amount	1,500	1,500
Accumulated Amortization	$ 392	$ 292

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Summary of Gross Amounts and Accumulated Amortization of Identifiable Intangible Assets (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, useful life	15 years
Minimum [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, useful life	6 years
Minimum [Member] | Covenants not-to-Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, useful life	4 years
Maximum [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, useful life	15 years
Maximum [Member] | Covenants not-to-Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, useful life	6 years

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill And Intangible Assets Disclosure [Abstract]
Amortization expense for intangible assets	$ 1.4	$ 1.4	$ 1.7

Goodwill and Other Intangible_7

Goodwill and Other Intangible Assets - Summary of Estimated Amortization Expense (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
2,019	$ 1,180
2,020	1,163
2,021	1,163
2,022	1,008
2,023	$ 853

Computation of Earnings Per S_3

Computation of Earnings Per Share - Summary of Calculation of Basic Earnings Per Common Share and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Numerator:
Net income	$ 25,380	$ 28,195	$ 30,281	$ 21,125	$ 47,789	$ 14,373	$ 17,571	$ 11,395	$ 104,981	$ 91,129	$ 48,024
Denominator:
Denominator for basic earnings per share–weighted average common shares									25,762	25,518	25,038
Effect of dilutive stock options and restricted stock									160	142	51
Effect of other common stock equivalents									369	426	591
Denominator for diluted earnings per share–adjusted weighted average common shares									26,291	26,086	25,680
Basic Earnings Per Share	$ 0.98	$ 1.09	$ 1.18	$ 0.82	$ 1.87	$ 0.56	$ 0.69	$ 0.45	$ 4.08	$ 3.57	$ 1.92
Diluted Earnings Per Share	$ 0.97	$ 1.07	$ 1.15	$ 0.80	$ 1.82	$ 0.55	$ 0.68	$ 0.44	$ 3.99	$ 3.49	$ 1.87

Computation of Earnings Per S_4

Computation of Earnings Per Share - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Common stock excluded from the calculation of diluted earnings per share	45,150	61,364

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Purchase and Sale of Common Stock (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Shares of common stock purchased	10,390	8,220	11,530
Aggregate purchase price of shares purchased	$ 700,234	$ 390,542	$ 291,349
Shares of common stock sold	37,086	4,717	10,694
Aggregate sale price of shares sold	$ 2,777,630	$ 271,417	$ 322,928

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - shares	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Shares reserved for issuance under the Directors Deferred Fee Plan	240,000	228,423

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)Employee$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Feb. 22, 2019shares	Feb. 22, 2018shares	Feb. 24, 2017shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Associated cash flows from financing activities | $			$ 500
Associated cash flows from operating activities | $	$ 600	$ 1,700
Restricted stock vesting period	3 years
Stock-based compensation | $	$ 5,619	5,083	4,599
Unrecognized compensation expense | $	$ 2,800
Weighted average recognition period of compensation expenses	1 year 10 months 24 days
Total intrinsic value of options exercised | $	$ 3,500	$ 3,500	$ 2,500
Weighted-average grant-date fair value per share of options granted | $ / shares	$ 23.74	$ 15.49	$ 9.99
Weighted-average grant-date fair value per share of options vested | $ / shares	$ 15.41	$ 12.26	$ 12.95
After three years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting percentage	25.00%
After four years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting percentage	25.00%
After five years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting percentage	50.00%
January 2016 - December 2018 [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range				128,240
January 2015 - December 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range					49,188
January 2014 - December 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range						30,893
Stock Option and Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation | $	$ 2,100	$ 2,300	$ 2,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	3 years
Restricted Stock [Member] | After three years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	3 years
Restricted Stock [Member] | After four years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	4 years
Restricted Stock [Member] | After five years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	5 years
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	3 years
Operating expense | $	$ 2,400	$ 1,900	$ 1,600
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range	128,240
Maximum [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	5 years
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range	0
Minimum [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	3 years
Non Employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual service	3 years
Contractual term	7 years
Shares issued to non employee director	1,363	1,942	3,279
2018 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved	1,100,000
Reserved and unissued shares	1,100,000
2018 Omnibus Incentive Plan [Member] | Non Employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual grant of shares	0
2011 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved	2,350,000
Additional grant under Plan	0
Restricted stock vesting period	3 years
Reserved and unissued shares	637,695	756,218
Maximum member of management and executive employees eligible for awards | Employee	20
2011 Omnibus Incentive Plan [Member] | Non Employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual grant of shares	0
2011 Omnibus Incentive Plan [Member] | Non Employee Director [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual grant of shares	12,000
2003 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved	1,236,000
Additional grant under Plan	0
Reserved and unissued shares	0	0
Directors' Deferred Fee Plan [Member] | Non Employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units issued in lieu of cash compensation to non employee directors	11,577	15,152	23,734

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning balance, options	335,000
Granted, options	46,500
Exercised, options	(105,860)
Forfeited, options	(9,330)
Ending balance, options	266,310
Exercisable options, ending balance	8,830
Beginning balance, weighted average exercise price | $ / shares	$ 34.75
Ending balance, weighted average exercise price | $ / shares	38.93
Exercisable, weighted average exercisable price | $ / shares	$ 43.01
Outstanding, weighted average remaining contractual life (years)	4 years 7 months 6 days
Exercisable, weighted average remaining contractual life (years)	3 years 1 month 6 days
Outstanding, aggregate intrinsic value | $	$ 5,289
Exercisable, aggregate intrinsic value | $	$ 113

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Weighted Average Assumptions Used In Valuing Options (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk free interest rate	2.24%	1.89%	1.63%
Expected life in years	4 years 2 months 12 days	4 years 6 months	4 years 6 months
Expected volatility	36.31%	36.90%	41.42%

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Unvested Option (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Unvested, options beginning balance	309,720
Granted, options	46,500
Vested, options	(89,410)
Forfeited, options	(9,330)
Unvested, options ending balance	257,480	309,720
Unvested , weighted average grant date fair value beginning balance	$ 12.38
Granted, weighted average grant date fair value	23.74	$ 15.49	$ 9.99
Vested, weighted average grant date fair value	15.41	12.26	$ 12.95
Forfeited, weighted average grant date fair value	13
Unvested , weighted average grant date fair value ending balance	$ 13.36	$ 12.38

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted Stock [Member]	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, options beginning balance | shares	57,857
Granted, options | shares	16,562
Vested, options | shares	(2,896)
Forfeited, options | shares	(1,162)
Unvested, options ending balance | shares	70,361
Unvested, weighted average grant date fair value beginning balance | $ / shares	$ 42.10
Granted | $ / shares	73.35
Vested | $ / shares	47.46
Forfeited | $ / shares	57.48
Unvested, weighted average grant date fair value ending balance | $ / shares	$ 48.98

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Shares held by the Rabbi trust	143,614	170,310
Performance incentives	$ 19.9	$ 12.2	$ 5.1
Shares purchased by custodians	6,840	8,063	20,532
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Payroll deduction for ESPP, percent of annual wages	10.00%
Highly Compensated Employees [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Payroll deduction for ESPP, percent of annual wages	20.00%
401(k)Saving Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Company match of contribution	50.00%
Employees contribution share	6.00%
Contribution in operation	$ 9.9	$ 8.3	$ 7.1

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax [Line Items]
Federal corporate tax rate	21.00%	35.00%
Benefit recognized from tax cuts and jobs act		$ 33,910,000
Interest related to unrecognized tax benefits	$ 0	0	$ 100,000
Accrued interest and penalties related to unrecognized tax benefits	100,000	100,000
Unrecognized tax benefits that would affect the Company's effective tax rate if recognized	900,000	1,100,000
Cash (received) paid for income taxes	1,900,000	17,000,000	5,400,000
Tax credit recognized	$ 1,000,000		$ 1,000,000
Accounting Standards Update 2016-09 [Member]
Income Tax [Line Items]
Benefit related to excess tax benefits from stock activity		$ 1,700,000
Maximum [Member]
Income Tax [Line Items]
Income tax year open for examination	2,018
Maximum [Member] | State and Local Jurisdiction [Member]
Income Tax [Line Items]
Income tax year open for examination	2,018
Minimum [Member]
Income Tax [Line Items]
Income tax year open for examination	2,015
Minimum [Member] | State and Local Jurisdiction [Member]
Income Tax [Line Items]
Income tax year open for examination	2,009

Income Taxes - Summary of Defer

Income Taxes - Summary of Deferred Tax Liabilities and Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Depreciation	$ 115,775	$ 86,506
Other	2,977	93
Gross deferred tax liabilities	118,752	86,599
Allowance for doubtful accounts	(995)	(988)
Equity-based compensation	(3,444)	(2,607)
Employee benefits	(6,139)	(5,458)
Claims and insurance	(17,176)	(16,929)
Other	(4,105)	(1,194)
Gross deferred tax assets	(31,859)	(27,176)
Net deferred tax liability	$ 86,893	$ 59,423

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Tax Provision (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
U.S. federal	$ 1,650	$ 17,637	$ 12,127
State	1,732	1,761	1,988
Total current income tax provision	3,382	19,398	14,115
Deferred:
U.S. federal	27,114	(21,221)	12,599
State	356	445	181
Total deferred income tax provision	27,470	(20,776)	12,780
Total income tax provision	$ 30,852	$ (1,378)	$ 26,895

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation Between Income Taxes and Effective Income Tax Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Provision at federal statutory rate	$ 28,525	$ 31,422	$ 26,222
State income taxes, net	4,468	2,545	2,418
Tax Cuts and Jobs Act benefit		(33,910)
Nondeductible business expenses (benefits)	(49)	(913)	462
Tax credits	(1,659)	(190)	(1,278)
Other, net	(433)	(332)	(929)
Total income tax provision	$ 30,852	$ (1,378)	$ 26,895

Income Taxes - Summary of Gross

Income Taxes - Summary of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits at beginning of year	$ 1,093	$ 1,280
Gross decreases in tax positions for prior years	(341)	(7)
Gross increases in tax positions for current year	319	171
Lapse of statute of limitations	(202)	(351)
Gross unrecognized tax benefits at end of year	$ 869	$ 1,093

Summary of Quarterly Operatin_3

Summary of Quarterly Operating Results (Unaudited) - Summary of Quarterly Operating Results (Unaudited) (Detail) - 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
Income Statement [Abstract]
Operating revenue	$ 406,750	$ 425,562	$ 428,732	$ 392,805	$ 360,196	$ 357,010	$ 364,404	$ 323,090	$ 1,653,849	$ 1,404,703	$ 1,250,391
Operating income	33,336	38,697	41,565	27,579	22,928	24,568	29,686	17,527	141,177	94,710	79,136
Net income	$ 25,380	$ 28,195	$ 30,281	$ 21,125	$ 47,789	$ 14,373	$ 17,571	$ 11,395	$ 104,981	$ 91,129	$ 48,024
Basic earnings per share	$ 0.98	$ 1.09	$ 1.18	$ 0.82	$ 1.87	$ 0.56	$ 0.69	$ 0.45	$ 4.08	$ 3.57	$ 1.92
Diluted earnings per share	$ 0.97	$ 1.07	$ 1.15	$ 0.80	$ 1.82	$ 0.55	$ 0.68	$ 0.44	$ 3.99	$ 3.49	$ 1.87

Valuation and Qualifying Acco_3

Valuation and Qualifying Accounts - Summary of Valuation and Qualifying Accounts (Detail) - Allowance for Uncollectible Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance, beginning of period	$ 3,991	$ 3,222	$ 3,451
Additions - Charged to costs and expenses	1,978	2,634	1,475
Deductions	(1,941)	(1,865)	(1,704)
Balance, end of period	$ 4,028	$ 3,991	$ 3,222