Saia (SAIA) 10-K 27 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 26, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	SAIA
Entity Registrant Name	SAIA INC
Entity Central Index Key	1177702
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		25,089,833
Entity Public Float			$1,066,074,449

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current Assets:
Cash and cash equivalents	$4,367	$159
Accounts receivable, less allowances of $3,868 in 2014, and $3,737 in 2013	128,367	117,937
Prepaid expenses and other	13,687	13,156
Deferred income taxes	19,460	20,421
Income tax receivable	18,335	13,497
Other current assets	5,420	5,083
Total current assets	189,636	170,253
Property and Equipment, at cost	891,145	797,527
Less-accumulated depreciation	407,505	365,301
Net property and equipment	483,640	432,226
Goodwill	5,231	5,231
Identifiable Intangibles, net	2,943	3,558
Other Noncurrent Assets	4,995	5,533
Total assets	686,445	616,801
Current Liabilities:
Accounts payable	42,388	50,799
Wages, vacations and employees' benefits	28,777	35,248
Claims and insurance accruals	29,314	27,637
Other current liabilities	20,862	20,030
Current portion of long-term debt	9,138	7,143
Total current liabilities	130,479	140,857
Other Liabilities:
Long-term debt, less current portion	73,897	69,740
Deferred income taxes	78,406	69,916
Claims, insurance and other	36,757	31,496
Total other liabilities	189,060	171,152
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, 24,871,806 and 24,478,544 shares issued and outstanding at December 31, 2014 and 2013, respectively	25	24
Additional paid-in-capital	223,713	213,648
Deferred compensation trust, 193,607 and 201,936 shares of common stock at cost at December 31, 2014 and 2013, respectively	-2,189	-2,246
Retained earnings	145,357	93,366
Total stockholders' equity	366,906	304,792
Total liabilities and stockholders' equity	$686,445	$616,801

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Allowance of accounts receivable	$3,868	$3,737
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	50,000	50,000
Preferred stock, shares issued
Preferred stock, shares outstanding
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	24,871,806	24,478,544
Common stock, shares outstanding	24,871,806	24,478,544
Deferred compensation trust	193,607	201,936

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Operating Revenue	$1,272,321	$1,139,094	$1,098,679
Operating Expenses:
Salaries, wages and employees' benefits	639,633	572,487	546,755
Purchased transportation	99,610	72,975	74,521
Fuel, operating expenses and supplies	314,788	306,364	308,176
Operating taxes and licenses	36,028	36,513	38,283
Claims and insurance	37,563	25,494	24,712
Depreciation and amortization	59,022	51,564	47,985
Operating gains, net	-16	-721	-487
Total operating expenses	1,186,628	1,064,676	1,039,945
Operating Income	85,693	74,418	58,734
Nonoperating Expenses (Income):
Interest expense	4,564	6,490	7,807
Other, net	-99	-217	-212
Nonoperating expenses, net	4,465	6,273	7,595
Income Before Income Taxes	81,228	68,145	51,139
Income Tax Expense	29,237	24,518	19,091
Net Income	$51,991	$43,627	$32,048
Weighted average common shares outstanding - basic	24,505	24,154	23,823
Weighted average common shares outstanding - diluted	25,463	25,205	24,815
Basic Earnings Per Share	$2.12	$1.81	$1.35
Diluted Earnings Per Share	$2.04	$1.73	$1.29

Consolidated_Statements_of_Sto

Consolidated Statements of Stockholders' Equity (USD $)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Deferred Compensation Trust [Member]	Retained Earnings [Member]
In Thousands, except Share data
Beginning Balance at Dec. 31, 2011	$219,301	$24	$203,785	($2,199)	$17,691
Beginning Balance, Shares at Dec. 31, 2011		23,906,732
Stock compensation for options and long-term incentives	2,089		2,089
Stock compensation for options and long-term incentives, Shares		40,152
Director deferred shares for annual deferral elections	599		599
Exercise of stock options, including tax benefits	913		913
Exercise of stock options, including tax benefits, Shares		91,748
Shares issued for long-term incentive awards net of shares withheld for taxes	-288		-288
Shares issued for long-term incentive awards net of shares withheld for taxes, Shares		49,785
Deferred tax adjustment for long-term incentive plan	-191		-191
Purchase of shares by Deferred Compensation Trust	-159			-159
Sale of shares by Deferred Compensation Trust	207		62	145
Net income	32,048				32,048
Ending Balance at Dec. 31, 2012	254,519	24	206,969	-2,213	49,739
Ending Balance, Shares at Dec. 31, 2012		24,088,417
Stock compensation for options and long-term incentives	2,227		2,227
Stock compensation for options and long-term incentives, Shares		16,499
Director deferred shares for annual deferral elections	674		674
3 for 2 Stock Split	-40		-40
3 for 2 Stock Split, Shares		-864
Exercise of stock options, including tax benefits	4,173		4,173
Exercise of stock options, including tax benefits, Shares		263,064
Shares issued for long-term incentive awards net of shares withheld for taxes	-1,162		-1,162
Shares issued for long-term incentive awards net of shares withheld for taxes, Shares		111,428
Deferred tax adjustment for long-term incentive plan	774		774
Purchase of shares by Deferred Compensation Trust	-158			-158
Sale of shares by Deferred Compensation Trust	158		33	125
Net income	43,627				43,627
Ending Balance at Dec. 31, 2013	304,792	24	213,648	-2,246	93,366
Ending Balance, Shares at Dec. 31, 2013		24,478,544
Stock compensation for options and long-term incentives	3,393		3,393
Stock compensation for options and long-term incentives, Shares		6,023
Director deferred shares for annual deferral elections	773		773
Exercise of stock options, including tax benefits	6,652	1	6,651
Exercise of stock options, including tax benefits, Shares	320,625	318,321
Shares issued for long-term incentive awards net of shares withheld for taxes	-1,667		-1,667
Shares issued for long-term incentive awards net of shares withheld for taxes, Shares		68,918
Deferred tax adjustment for long-term incentive plan	971		971
Purchase of shares by Deferred Compensation Trust	-53			-53
Sale of shares by Deferred Compensation Trust	54		-56	110
Net income	51,991				51,991
Ending Balance at Dec. 31, 2014	$366,906	$25	$223,713	($2,189)	$145,357
Ending Balance, Shares at Dec. 31, 2014		24,871,806

Consolidated_Statements_of_Sto1

Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Tax benefits exercise stock options	$2,984	$1,356	$23
Common Stock [Member]
Tax benefits exercise stock options	2,984	1,356	23
Additional Paid-in Capital [Member]
Tax benefits exercise stock options	$2,984	$1,356	$23

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities:
Net income	$51,991	$43,627	$32,048
Noncash items included in net income:
Depreciation and amortization	59,022	51,564	47,985
Provision for doubtful accounts	1,942	2,227	1,833
Deferred income taxes	9,462	12,098	-705
Gain from property disposals, net	-17	-721	-487
Stock-based compensation	4,166	2,902	2,687
Changes in operating assets and liabilities:
Accounts receivable	-12,372	-13,350	538
Accounts payable	-8,590	5,479	3,362
Other working capital items, net	-11,215	-5,213	13,972
Claims, insurance and other	5,260	392	-448
Other, net	2,521	2,307	-110
Net cash provided by operating activities	102,170	101,312	100,675
Investing Activities:
Acquisition of property and equipment	-97,750	-126,358	-86,120
Proceeds from disposal of property and equipment	2,905	4,338	3,305
Acquisition of business, net of cash received			-7,616
Net cash used in investing activities	-94,845	-122,020	-90,431
Financing Activities:
Repayment of revolving credit agreement	-340,540	-223,798	-344,867
Borrowing of revolving credit agreement	337,223	262,125	354,857
Repayment of long-term debt	-7,143	-22,143	-22,143
Other Financing Activity	-280	-586
Proceeds on stock option exercises (including excess tax benefits)	7,623	4,948	913
Net cash (used in) provided by financing activities	-3,117	20,546	-11,240
Net Increase (Decrease) in Cash and Cash Equivalents	4,208	-162	-996
Cash and cash equivalents, beginning of year	159	321	1,317
Cash and cash equivalents, end of year	4,367	159	321
Non Cash Investing Activities
Equipment financed with capital leases	$16,886

Description_of_Business_and_Su

Description of Business and Summary of Accounting Policies	12 Months Ended
	Dec. 31, 2014
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. The Company offers customers a wide range of less-than-truckload, non-asset truckload, expedited and logistics services across the United States through its wholly-owned subsidiaries. Effective December 31, 2014, the Company’s subsidiaries were as follows: Saia Motor Freight Line, LLC, doing business as Saia LTL Freight; Saia TL Plus, LLC, formerly Robart Transportation, Inc., Saia Sales, LLC, and Saia Logistics Services, LLC, formerly The RL Services Group, LLC.
	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.
	Common Stock Split
	On May 16, 2013, the Company announced a three-for-two stock split which was effected in the form of a 50 percent stock dividend. The shares were distributed on June 13, 2013 to shareholders of record as of the close of business on the record date of May 31, 2013. In lieu of fractional shares, shareholders received a cash payment based on the closing share price of the Company’s common stock on the record date. All references in this report to common shares outstanding, weighted average common shares and earnings per share amounts have been retroactively restated to reflect this stock split.
	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.
	New Accounting Pronouncements
	On May 28, 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services. The ASU will replace most existing revenue recognition guidance in U.S. generally accepted accounting principles when it becomes effective. The new standard is effective for us on January 1, 2017. Early application is not permitted. The standard permits the use of either the retrospective or cumulative effect transition method. The Company is evaluating the effect that ASU 2014-09 will have on its consolidated financial statements and related disclosures. The Company has not yet selected a transition method nor has it completed its evaluation of the effect of the standard on its ongoing financial reporting.
	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.
	Inventories, fuel and operating supplies:    Inventories are carried at average cost and included in other current assets. To mitigate the Company’s risk to rising fuel prices, the Company has implemented fuel surcharge programs and considers effects of these fuel surcharge programs in customer pricing negotiations.
	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		8 to 10
	Trailers		10 to 14
	Other revenue equipment		10 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):
		2014		2013
	Land	$	53,632	$	52,745
	Structures		140,206		115,874
	Tractors		290,717		273,129
	Trailers		237,262		202,173
	Other revenue equipment		37,220		34,616
	Technology equipment and software		63,773		58,957
	Other		68,334		60,033
	Total property and equipment, at cost	$	891,145	$	797,527
	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 and freight management. Depreciation was $58.4 million, $51.0 million and $47.5 million for the years ended December 31, 2014, 2013 and 2012, respectively. Depreciation and amortization expense includes amortization of assets under capital lease.
	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, 2014, 2013, and 2012, the Company capitalized $1.0 million, $2.1 million, and $1.0 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 for self-funded retention are included in claims and insurance reserves based on 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. The former parent of Saia provides guarantees for claims in certain self-insured states that arose prior to September 30, 2002 (See Note 12 for more information regarding the guarantees).
	Risk retention amounts per occurrence during the three years ended December 31, 2014, were as follows:
	Workers’ compensation	$	1,000,000
	Bodily injury and property damage		2,000,000
	Employee medical and hospitalization		350,000
	Cargo loss and damage		250,000
	The Company’s insurance accruals are presented net of amounts receivable from insurance companies that provide coverage above the Company’s retention.
	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 the income taxes Topic of Financial Accounting Standards Board (FASB) Account 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 Income Taxes 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 is recognized on a percentage-of-completion basis for shipments in transit while expenses are recognized as incurred.
	Stock-Based Compensation:    The Company accounts for its employee stock-based compensation awards in accordance with ASC 718, Compensation-Stock Compensation. 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-Sholes-Merton model to estimate the fair value of stock options 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 6.0 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, Property, Plant, and Equipment, 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 Accounting Standards Update (“ASU”) 2011-08, “Testing Goodwill for Impairment.” In accordance with this ASU, codified in the “Intangibles, Goodwill, and Other” topic of the FASB Accounting Standards Codification, the Company first performs a qualitative assessment to determine whether it is necessary to perform the two-step goodwill impairment test required by the previous standard. The Company is not required to estimate the fair value of a reporting unit unless the Company determines, based on qualitative assessment, that it is more likely than not that its fair value is less than its carrying amount.
	Advertising:    The costs of advertising are expensed as incurred. Advertising costs charged to expense were $1.9 million, $0.8 million, and $0.7 million in 2014, 2013 and 2012, 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, 2014 and 2013, because of the relatively short maturity of these instruments. See Note 2 for fair value disclosures related to long-term debt.

Debt_and_Financing_Arrangement

Debt and Financing Arrangements	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Debt and Financing Arrangements	2.    Debt and Financing Arrangements
	At December 31, debt consisted of the following (in thousands):
		December 31,		December 31,
		2014		2013
	Credit Agreement with Banks, described below	$	45,000	$	48,312
	Senior Notes under a Master Shelf Agreement, described below		21,429		28,571
	Capital Leases, described below		16,606		—
	Total debt		83,035		76,883
	Less: current portion of long-term debt		9,138		7,143
	Long-term debt, less current portion	$	73,897	$	69,740
	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 Restated Credit Agreement) with a group of banks to fund capital investments, letters of credit and working capital needs. The facility provides up to $200 million in availability, subject to a borrowing base and expires in June 2018. The Company is also a party to a long-term note agreement (the Restated Master Shelf Agreement). The Company has pledged certain real estate and facilities, tractors and trailers, accounts receivable and other assets to secure indebtedness under both agreements.
	Restated Credit Agreement
	The Restated Credit Agreement is a revolving credit facility for up to $200 million expiring in June 2018. The Restated Credit Agreement also has an accordion feature that allows for an additional $40 million of availability, subject to lender approval. The Restated Credit Agreement provides for a LIBOR rate margin range from 125 basis points to 250 basis points, base rate margins from minus 12.5 to plus 50 basis points, letter of credit fee range from 137.5 basis points to 262.5 basis points and an unused portion fee from 20 basis points to 32.5 basis points in each case based on the Company’s leverage ratio.
	Under the Restated Credit Agreement, the Company must maintain certain financial covenants including a minimum fixed charge coverage ratio, a maximum leverage ratio and a minimum tangible net worth, among others. The Restated Credit Agreement also provides for a pledge by the Company of certain land and structures, certain tractors, trailers and other personal property and accounts receivable, as defined in the Restated Credit Agreement. Total bank commitments under the Restated Credit Agreement are $200 million subject to a borrowing base calculated utilizing certain pledged property, equipment and accounts receivable as defined in the Restated Credit Agreement.
	At December 31, 2014, the Company had borrowings of $45.0 million and outstanding letters of credit of $47.3 million under the Restated Credit Agreement. At December 31, 2013, the Company had borrowings of $48.3 million and outstanding letters of credit of $59.1 million under the Restated Credit Agreement. The available portion of the Restated Credit Agreement may be used for general corporate purposes, including future capital expenditures, working capital and letter of credit requirements as needed.
	Restated Master Shelf Agreement
	On September 20, 2002, the Company issued $100 million in Senior Notes under a $125 million (amended to $150 million in April 2005) Master Shelf Agreement with Prudential Investment Management, Inc. and certain of its affiliates. The Company issued another $25 million in Senior Notes on November 30, 2007 and $25 million in Senior Notes on January 31, 2008 under the same Master Shelf Agreement.
	The initial $100 million Senior Notes had a fixed interest rate of 7.38 percent. Payments due under the $100 million Senior Notes were interest only until June 30, 2006 and at that time semi-annual principal payments began with the final payment made in December 2013. The November 2007 issuance of $25 million Senior Notes has a fixed interest rate of 6.14 percent. The January 2008 issuance of $25 million Senior Notes has a fixed interest rate of 6.17 percent. Payments due for both $25 million issuances were interest only until June 30, 2011 and at that time semi-annual principal payments began with the final payments due January 1, 2018. Under the terms of the Senior Notes, the Company must maintain certain financial covenants including a minimum fixed charge coverage ratio, a maximum leverage ratio and a minimum tangible net worth, among others.
	Capital Leases
	The Company is obligated under capital leases which include obligations covering revenue equipment totaling $16.6 million that expire in seven years. Amortization of assets held under the capital leases is included in depreciation expense. The weighted average interest rate for the capital leases at December 31, 2014 is 2.92%.
	Other
	The Company paid cash for interest of $4.5 million, $6.1 million, and $7.3 million for the years ended December 31, 2014, 2013 and 2012, respectively.
	The estimated fair value of total debt at December 31, 2014 and 2013 is $83.7 million and $78.0 million, respectively, based upon level two in the fair value hierarchy. The fair value of these senior notes is based on undiscounted cash flows at market interest rates for similar issuances of private debt.
	The principal maturities of long-term debt for the next five years (in thousands) are as follows:
		Amount
	2015	$	9,504
	2016		9,596
	2017		9,596
	2018		47,453
	2019		2,453
	Thereafter		6,330
	Total	$	84,932
	Less: Amounts Representing Interest on Capital Leases		1,897
	Total	$	83,035

Commitments_Contingencies_and_

Commitments, Contingencies and Uncertainties	12 Months Ended
	Dec. 31, 2014
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 $17.1 million, $17.9 million, and $17.7 million for the years ended December 31, 2014, 2013 and 2012, respectively.
	At December 31, 2014, the Company was committed under non-cancellable operating lease agreements requiring minimum annual rentals payable as follows (in thousands):
		Amount
	2015	$	14,051
	2016		11,215
	2017		9,780
	2018		7,460
	2019		5,291
	Thereafter		12,778
	Total	$	60,575
	Management expects that in the normal course of business, leases will be renewed or replaced as they expire.
	Capital expenditures committed were $74.4 million at December 31, 2014. As of December 31, 2014 and 2013, the Company had $1.8 million and $1.6 million, respectively, of capital expenditures in accounts payable.
	Other.    The Company is subject to legal proceedings that arise in the ordinary course of its business. The Company 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_

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2014
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, 2012	$	5,231
	No Activity		—
	December 31, 2013		5,231
	No Activity		—
	December 31, 2014	$	5,231
	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, 2014				December 31, 2013
		Gross		Accumulated		Gross		Accumulated
		Amount		Amortization		Amount		Amortization
	Amortizable intangible assets:
	Customer relationships (useful life of 6-10 years)	$	7,700	$	4,795	$	7,700	$	4,195
	Covenants not-to-compete (useful life of 4-6 years)		3,625		3,587		3,625		3,572
		$	11,325	$	8,382	$	11,325	$	7,767
	Amortization expense for intangible assets was $0.6 million for 2014, $0.6 million for 2013, and $0.5 million for 2012. Estimated amortization expense for the five succeeding years follows (in thousands):
		Amount
	2015	$	615
	2016		615
	2017		317
	2018		310
	2019		310
	Total	$	2,167

Computation_of_Earnings_Per_Sh

Computation of Earnings Per Share	12 Months Ended
	Dec. 31, 2014
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):
		Years Ended December 31,
		2014		2013		2012
	Numerator:
	Net income	$	51,991	$	43,627	$	32,048
	Denominator:
	Denominator for basic earnings per share — weighted average common shares		24,505		24,154		23,823
	Effect of dilutive stock options		239		297		180
	Effect of other common stock equivalents		719		754		812
	Denominator for diluted earnings per share — adjusted weighted average common shares		25,463		25,205		24,815
	Basic Earnings Per Share	$	2.12	$	1.81	$	1.35
	Diluted Earnings Per Share	$	2.04	$	1.73	$	1.29
	In 2014 and 2013, options and restricted stock for 7,936, and 143,640 shares of common stock 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, 2014
Equity [Abstract]
Stockholders' Equity	6.    Stockholders’ Equity
	Share and per share amounts have been retroactively restated to reflect the three-for-two common stock split effected in 2013.
	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:
		Years ended December 31,
		2014		2013		2012
	Shares of common stock purchased		1,400		5,900		13,650
	Aggregate purchase price of shares purchased	$	52,961	$	158,060	$	158,883
	Shares of common stock sold		9,729		11,719		14,882
	Aggregate sale price of shares sold	$	53,962	$	158,060	$	206,794
	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 244,835 and 228,546 shares reserved for issuance under the Directors’ Deferred Fee Plan at December 31, 2014 and 2013, respectively. The shares reserved for issuance under the Directors’ Deferred Fee Plan are treated as common stock equivalents in computing diluted earnings per share.

StockBased_Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	7.    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 a cost in the financial statements and that for equity-classified awards such costs are measured at the grant date fair value of the award. The Company uses a Black-Scholes-Merton model to estimate the fair value of stock options granted to employees and expects to continue to use this option valuation model under ASC 718.
	ASC 718 also requires 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 reduces net operating cash flows and increases net financing cash flows. For the years ended December 31, 2014, 2013 and 2012, cash flows from financing activities were increased by $4.0 million, $2.1 million, and $0.1 million, respectively, for such excess tax deductions.
	The stockholders of the Company approved the First 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 2011 Omnibus Plan has a total of 2,025,000 shares reserved. 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 and by the terms of the Plan, no new grants may be made after January 22, 2013.
	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; 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 have cliff vesting at the end of three years of continuous service and have a seven-year contractual term. The non-employee director stock options issued under the 2003 Omnibus Plan expire ten years from the date of grant; are exercisable six months after the date of grant; and have an exercise price equal to the fair market value of the Company’s common stock on the date of grant. No stock options have been granted to non-employee directors under the 2011 Omnibus Plan.
	The 2011 Omnibus Plan provides 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 1,905, 2,199, and 4,063 for the years ended December 31, 2014, 2013 and 2012, respectively. Non-employee directors were also issued 16,561, 24,191 and 40,398 units equivalent to shares in the Company’s common stock under the Directors’ Deferred Fee Plan during the years ended December 31, 2014, 2013 and 2012, respectively.
	At December 31, 2014 and 2013, zero and 158,700 shares remain reserved and unissued under the provisions of the 2003 Omnibus Plan, all of which are allocated to outstanding Performance Unit Awards and outstanding stock options described below. At December 31, 2014, 1,257,996 shares remain reserved and unissued under the provisions of the 2011 Omnibus Plan, a portion of which are allocated to outstanding Performance Unit Awards and outstanding stock options and restricted stock described below. The Company has historically issued new shares to satisfy stock option exercises or other awards issued under the 2011 Omnibus Plan and 2003 Omnibus Plan.
	The years ended December 31, 2014, 2013 and 2012 had stock option and restricted stock compensation expense of $2.2 million, $1.2 million and $1.1 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, 2014, there is unrecognized compensation expense of $2.2 million related to unvested stock options and restricted stock, which is expected to be recognized over a weighted average period of 2.1 years.
	The following table summarizes the activity of stock options for the year ended December 31, 2014 for both employees and non-employee directors:
		Options			Weighted			Weighted			Aggregate
					average			Average			Intrinsic
					exercise price			Remaining			Value
								Contractual			(000’s)
								Life (years)
	Outstanding at December 31, 2013		588,510		$	14.76
	Granted		116,240
	Exercised		(320,625	)
	Forfeited		(24,750	)
	Expired		—
	Outstanding at December 31, 2014		359,375		$	22.03			5.1		$	11,975
	Exercisable at December 31, 2014		—		$	—			—		$	—
	The total intrinsic value of options exercised during the years ended December 31, 2014, 2013 and 2012 was $9.9 million, $4.7 million, and $0.4 million, respectively. The weighted-average grant-date fair value per share of options granted during the years ended December 31, 2014, 2013 and 2012 was $12.12, $12.95, and $5.57, respectively. The weighted-average grant-date fair value per share of shares vested during the years ended December 31, 2014, 2013 and 2012 was $6.75, $4.15, and $4.25, respectively.
	The following table summarizes the weighted average assumptions used in valuing options for the years ended December 31, 2014, 2013 and 2012:
		2014			2013			2012
	Risk free interest rate		1.58	%		0.8	%		0.84	%
	Expected life in years		4.5			4.5			5
	Expected volatility		44.33	%		58.5	%		59.82	%
	Dividend rate		—			—			—
	The risk-free 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, 2014 and changes during the year ended December 31, 2014:
		Options			Weighted average
					Grant-date Fair  Value
	Unvested at December 31, 2013		429,810		$	8.02
	Granted		116,240			12.12
	Vested		(161,925	)		6.75
	Forfeited		(24,750	)		9.46
	Unvested at December 31, 2014		359,375		$	9.82
	The Company granted shares of restricted stock to certain key executives in February 2013. On September 10, 2014, the Company awarded Frederick J. Holzgrefe, III, 7,936 restricted shares under the 2011 Omnibus Plan, in connection with him joining Saia as Vice President of Finance and Chief Financial Officer. All of the shares of restricted stock issued to executives to date 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. 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, 2014:
		Shares			Weighted average
					Grant-date Fair  Value
	Restricted Stock at December 31, 2013		122,731		$	11
	Granted		7,936		$	50.4
	Vested		(15,152	)	$	11
	Forfeited		(7,576	)	$	11
	Restricted Stock at December 31, 2014		107,939		$	13.9
	Performance Unit Awards
	Under the 2011 Omnibus Plan and the 2003 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 from continuing operations include expense for the performance unit awards of $1.2 million in 2014, and $1.0 million 2013 and 2012. Shares earned under the performance unit awards will be issued in the first quarter of the year following the end of the performance period. There was an issuance of 146,052 shares for the 2012-2014 performance period in February 2015, 106,330 shares for the February 2011-February 2014 performance period in February 2014, and 150,384 shares for the 2010-2012 performance period in February 2013. The issuance of shares related to these awards would range from zero to a maximum of 68,200 shares per year as of December 31, 2014.

Employee_Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2014
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 elected to temporarily suspend the Company match in February 2009. Effective April 1, 2011, the Company reinstated one-half of the 401(k) match with the remainder of the match reinstated on December 1, 2013. The Company’s total contributions included in continuing operations for the years ended December 31, 2014, 2013 and 2012, were $5.7 million, $2.5 million, and $2.1 million, respectively.
	Deferred Compensation Plan
	The Saia Executive Capital Accumulation 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 stock rather than cash. At December 31, 2014 and 2013, the Company’s Rabbi Trust, which holds the investments for the Capital Accumulation Plan, held 193,607 and 201,936 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 salaried and clerical employees which are based primarily on actual operating results achieved, compared to targeted operating results. Operating results from continuing operations include performance incentive accruals of $6.5 million, $8.8 million, and $8.4 million in 2014, 2013 and 2012, respectively. 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. The custodian uses the funds to purchase the Company’s common stock at current market prices. The custodian purchased 4,751, 6,711, and 13,830 shares in the open market during 2014, 2013 and 2012, respectively.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	9.    Income Taxes
	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):
		2014			2013
	Depreciation		100,607		$	88,522
	Other		(559	)		3,548
	Revenue		0			120
	Gross deferred tax liabilities		100,048			92,190
	Allowance for doubtful accounts		(1,511	)		(1,467	)
	Equity-based compensation		(3,440	)		(3,287	)
	Employee benefits		(7,024	)		(6,996	)
	Claims and insurance		(22,019	)		(19,374	)
	Other		(7,108	)		(11,571	)
	Gross deferred tax assets		(41,102	)		(42,695	)
	Net deferred tax liability	$	58,946		$	49,495
	The Company has determined that a valuation allowance related to deferred tax assets was not necessary at December 31, 2014 or 2013 since it is more likely than not the deferred tax assets will be realized from future reversals of temporary differences or future taxable income.
	The income tax provision for continuing operations consists of the following (in thousands):
		2014			2013			2012
	Current:
	U.S. federal	$	18,085		$	9,924		$	16,837
	State		1,690			2,496			2,959
	Total current income tax provision		19,775			12,420			19,796
	Deferred:
	U.S. federal		9,547			11,822			(678	)
	State		(85	)		276			(27	)
	Total deferred income tax (benefit) provision		9,462			12,098			(705	)
	Total income tax provision	$	29,237		$	24,518		$	19,091
	A reconciliation between income taxes at the federal statutory rate (35 percent) and the effective income tax provision is as follows:
		2014			2013			2012
	Provision at federal statutory rate	$	28,430		$	23,851		$	17,899
	State income taxes, net		2,426			2,574			2,025
	Nondeductible business expenses		589			675			503
	Tax credits		(1,434	)		(2,429	)		(253	)
	Other, net		(774	)		(153	)		(1,083	)
	Total provision	$	29,237		$	24,518		$	19,091
	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 2012-2014 remain open to examination. The expiration of the statute of limitations related to the various state income tax returns that the Company files vary by state. In general, tax years 2005-2013 remain open to examination by the various state and local jurisdictions. However, a state could challenge certain tax positions back to the 2001 tax year.
	A reconciliation of the beginning and ending total amounts of gross unrecognized tax benefits is as follows:
		2014			2013
	Gross unrecognized tax benefits at beginning of year	$	1,281		$	1,290
	Gross decreases in tax positions for prior years		—			—
	Gross increases in tax positions for current year		202			—
	Settlements		—			—
	Lapse of statute of limitations		(318	)		(9	)
	Gross unrecognized tax benefits at end of year	$	1,165		$	1,281
	The Company recognizes interest and penalties related to uncertain tax positions as a component of income tax expense. During the years ended December 31, 2014, 2013 and 2012, respectively, the Company recorded interest related to unrecognized tax benefits of approximately $0.3 million, $0.1 million, and $0.1 million, respectively. The Company had approximately $1.3 million, $1.6 million, and $1.4 million of accrued interest and penalties at December 31, 2014, 2013 and 2012, respectively. The total amount of unrecognized tax benefits that would affect the Company’s effective tax rate if recognized is $1.2 million and $1.3 million as of December 31, 2014 and 2013, respectively. The Company paid cash for income taxes of $20.8 million, $20.6 million, and $19.3 million in 2014, 2013 and 2012, 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.
	As a result of legislation enacted in January 2013, the Company recognized tax credits for 2012 alternative fuel usage of approximately $1.0 million in the first quarter of 2013.

Summary_of_Quarterly_Operating

Summary of Quarterly Operating Results (unaudited)	12 Months Ended
	Dec. 31, 2014
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, 2014	March 31		June 30		September 30		December 31
	Operating revenue	$	299,730	$	330,399	$	332,544	$	309,648
	Operating income		15,231		22,741		27,149		20,572
	Net income		8,576		13,568		16,278		13,569
	Basic earnings per share	$	0.35	$	0.55	$	0.66	$	0.55
	Diluted earnings per share	$	0.34	$	0.53	$	0.64	$	0.53
	Three months ended, 2013	31-Mar		30-Jun		30-Sep		31-Dec
	Operating revenue	$	273,795	$	292,557	$	293,087	$	279,655
	Operating income		14,532		23,259		21,935		14,692
	Net income		9,155		13,500		12,908		8,064
	Basic earnings per share	$	0.38	$	0.56	$	0.53	$	0.33
	Diluted earnings per share	$	0.37	$	0.54	$	0.51	$	0.32

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Acquisition	11.    Acquisition
	On July 2, 2012, Saia, Inc. acquired Robart Transportation, Inc. and its subsidiary, The RL Services Group, LLC (the Robart Companies). The acquired Robart Companies provide customers with non-asset truckload full service and logistics solutions. The purchase price of the acquisition was $7.9 million ($7.6 million, net of $0.3 million cash received) plus an earnout subject to performance of the acquired companies in 2013 up to a maximum of $1.3 million. The maximum earnout of $1.3 million was paid in February 2014. The Company believes the acquisition supports the strategic goal of diversifying Saia’s portfolio of service offerings.
	During the third quarter of 2012, the Company allocated the purchase price in excess of net tangible assets between tax deductible goodwill and other identifiable intangible assets related to the acquisition of the Robart Companies. The cash purchase price has been allocated based on independent appraisals and management’s estimates as follows (in thousands):
	Consideration:
	Cash	$	(7,934	)
	Contingent consideration arrangement		(1,162	)
	Fair value of total consideration transferred	$	(9,096	)
	Acquisition related costs included in SG&A		150
	Recognized amounts of identifiable assets acquired and liabilities assumed:
	Current assets	$	2,082
	Property and equipment		44
	Customer lists		3,184
	Current liabilities		(1,445	)
	Total identifiable net assets assumed	$	3,865
	Goodwill		5,231
	Total	$	9,096

RelatedParty_Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Related-Party Transactions	12.    Related-Party Transactions
	On September 30, 2002, YRC Worldwide, Inc. (Yellow) completed the spin-off of its 100 percent interest in the Company to Yellow stockholders (the Spin-off) in a tax-free distribution under Section 355 of the Internal Revenue Code. Subsequent to the Spin-off, Yellow continues to provide guarantees for certain pre-Spin-off workers’ compensation and casualty claims for which the Company is allocated its pro rata share of letters of credit which Yellow must maintain for these insurance programs. Yellow allocated $1.8 million and $1.6 million in letters of credit at December 31, 2014 and 2013 respectively, in connection with the Company’s insurance programs for which the Company pays quarterly Yellow’s cost plus 125 basis points.

Valuation_and_Qualifying_Accou

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2014
Valuation and Qualifying Accounts [Abstract]
Valuation and Qualifying Accounts	13.    Valuation and Qualifying Accounts
	For the Years Ended December 31, 2014, 2013 and 2012
	(in thousands)
					Additions
	Description		Balance,		Charged to		Charged		Deductions-(1)			Balance,
			beginning		costs and		to other					end of
			of period		expenses		accounts					period
	Year ended December 31, 2014:
	Deducted from asset account – Allowance for uncollectible accounts		$	3,737	$	1,942		—	($	1,811	)	$	3,868
	Year ended December 31, 2013:
	Deducted from asset account – Allowance for uncollectible accounts			3,881		2,227		—		(2,371	)		3,737
	Year ended December 31, 2012:
	Deducted from asset account – Allowance for uncollectible accounts			3,811		1,833		—		(1,763	)		3,881
	-1	Primarily uncollectible accounts written off — net of recoveries.

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2014
Subsequent Events [Abstract]
Subsequent Events	14.    Subsequent Events
	On February 2, 2015, subsequent to the end of the fourth quarter of 2014, the Company acquired LinkEx, Inc. The Company believes this acquisition is a future growth opportunity for its portfolio of services in the asset-light market. This acquisition fits into the Company’s strategic goal of diversifying Saia’s portfolio of service offerings. Pursuant to the terms of the purchase agreement, the Company paid a purchase price of approximately $25 million, subject, in part, to meeting profit targets.

Description_of_Business_and_Su1

Description of Business and Summary of Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Description of Business	Description of Business
	Saia, Inc. and its subsidiaries (Saia or the Company) are headquartered in Johns Creek, Georgia. The Company offers customers a wide range of less-than-truckload, non-asset truckload, expedited and logistics services across the United States through its wholly-owned subsidiaries. Effective December 31, 2014, the Company’s subsidiaries were as follows: Saia Motor Freight Line, LLC, doing business as Saia LTL Freight; Saia TL Plus, LLC, formerly Robart Transportation, Inc., Saia Sales, LLC, and Saia Logistics Services, LLC, formerly The RL Services Group, LLC.
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.
Common Stock Split	Common Stock Split
	On May 16, 2013, the Company announced a three-for-two stock split which was effected in the form of a 50 percent stock dividend. The shares were distributed on June 13, 2013 to shareholders of record as of the close of business on the record date of May 31, 2013. In lieu of fractional shares, shareholders received a cash payment based on the closing share price of the Company’s common stock on the record date. All references in this report to common shares outstanding, weighted average common shares and earnings per share amounts have been retroactively restated to reflect this stock split.
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.
New Accounting Pronouncements	New Accounting Pronouncements
	On May 28, 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services. The ASU will replace most existing revenue recognition guidance in U.S. generally accepted accounting principles when it becomes effective. The new standard is effective for us on January 1, 2017. Early application is not permitted. The standard permits the use of either the retrospective or cumulative effect transition method. The Company is evaluating the effect that ASU 2014-09 will have on its consolidated financial statements and related disclosures. The Company has not yet selected a transition method nor has it completed its evaluation of the effect of the standard on its ongoing financial reporting.
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.
Inventories, fuel and operating supplies	Inventories, fuel and operating supplies:    Inventories are carried at average cost and included in other current assets. To mitigate the Company’s risk to rising fuel prices, the Company has implemented fuel surcharge programs and considers effects of these fuel surcharge programs in customer pricing negotiations.
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		8 to 10
	Trailers		10 to 14
	Other revenue equipment		10 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):
		2014		2013
	Land	$	53,632	$	52,745
	Structures		140,206		115,874
	Tractors		290,717		273,129
	Trailers		237,262		202,173
	Other revenue equipment		37,220		34,616
	Technology equipment and software		63,773		58,957
	Other		68,334		60,033
	Total property and equipment, at cost	$	891,145	$	797,527
	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 and freight management. Depreciation was $58.4 million, $51.0 million and $47.5 million for the years ended December 31, 2014, 2013 and 2012, respectively. Depreciation and amortization expense includes amortization of assets under capital lease.
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, 2014, 2013, and 2012, the Company capitalized $1.0 million, $2.1 million, and $1.0 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 for self-funded retention are included in claims and insurance reserves based on 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. The former parent of Saia provides guarantees for claims in certain self-insured states that arose prior to September 30, 2002 (See Note 12 for more information regarding the guarantees).
	Risk retention amounts per occurrence during the three years ended December 31, 2014, were as follows:
	Workers’ compensation	$	1,000,000
	Bodily injury and property damage		2,000,000
	Employee medical and hospitalization		350,000
	Cargo loss and damage		250,000
	The Company’s insurance accruals are presented net of amounts receivable from insurance companies that provide coverage above the Company’s retention.
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 the income taxes Topic of Financial Accounting Standards Board (FASB) Account 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 Income Taxes 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: Revenue is recognized on a percentage-of-completion basis for shipments in transit while expenses are recognized as incurred.
Stock-Based Compensation	Stock-Based Compensation:    The Company accounts for its employee stock-based compensation awards in accordance with ASC 718, Compensation-Stock Compensation. 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-Sholes-Merton model to estimate the fair value of stock options 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 6.0 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, Property, Plant, and Equipment, 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 Accounting Standards Update (“ASU”) 2011-08, “Testing Goodwill for Impairment.” In accordance with this ASU, codified in the “Intangibles, Goodwill, and Other” topic of the FASB Accounting Standards Codification, the Company first performs a qualitative assessment to determine whether it is necessary to perform the two-step goodwill impairment test required by the previous standard. The Company is not required to estimate the fair value of a reporting unit unless the Company determines, based on qualitative assessment, that it is more likely than not that its fair value is less than its carrying amount.
Advertising	Advertising: The costs of advertising are expensed as incurred. Advertising costs charged to expense were $1.9 million, $0.8 million, and $0.7 million in 2014, 2013 and 2012, 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, 2014 and 2013, 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_Su2

Description of Business and Summary of Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
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		8 to 10
	Trailers		10 to 14
	Other revenue equipment		10 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):
		2014		2013
	Land	$	53,632	$	52,745
	Structures		140,206		115,874
	Tractors		290,717		273,129
	Trailers		237,262		202,173
	Other revenue equipment		37,220		34,616
	Technology equipment and software		63,773		58,957
	Other		68,334		60,033
	Total property and equipment, at cost	$	891,145	$	797,527
Summary of Risk Retention Amounts Per Occurrence	Risk retention amounts per occurrence during the three years ended December 31, 2014, were as follows:
	Workers’ compensation	$	1,000,000
	Bodily injury and property damage		2,000,000
	Employee medical and hospitalization		350,000
	Cargo loss and damage		250,000

Debt_and_Financing_Arrangement1

Debt and Financing Arrangements (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Summary of Reconciliation of Debt	At December 31, debt consisted of the following (in thousands):
		December 31,		December 31,
		2014		2013
	Credit Agreement with Banks, described below	$	45,000	$	48,312
	Senior Notes under a Master Shelf Agreement, described below		21,429		28,571
	Capital Leases, described below		16,606		—
	Total debt		83,035		76,883
	Less: current portion of long-term debt		9,138		7,143
	Long-term debt, less current portion	$	73,897	$	69,740
Schedule of Principal Maturities of Long-Term Debt	The principal maturities of long-term debt for the next five years (in thousands) are as follows:
		Amount
	2015	$	9,504
	2016		9,596
	2017		9,596
	2018		47,453
	2019		2,453
	Thereafter		6,330
	Total	$	84,932
	Less: Amounts Representing Interest on Capital Leases		1,897
	Total	$	83,035

Commitments_Contingencies_and_1

Commitments, Contingencies and Uncertainties (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Schedule of Non-Cancellable Capital And Operating Lease Agreements Requiring Minimum Annual Rentals Payable	At December 31, 2014, the Company was committed under non-cancellable operating lease agreements requiring minimum annual rentals payable as follows (in thousands):
		Amount
	2015	$	14,051
	2016		11,215
	2017		9,780
	2018		7,460
	2019		5,291
	Thereafter		12,778
	Total	$	60,575

Goodwill_and_Other_Intangible_1

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2014
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, 2012	$	5,231
	No Activity		—
	December 31, 2013		5,231
	No Activity		—
	December 31, 2014	$	5,231
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, 2014				December 31, 2013
		Gross		Accumulated		Gross		Accumulated
		Amount		Amortization		Amount		Amortization
	Amortizable intangible assets:
	Customer relationships (useful life of 6-10 years)	$	7,700	$	4,795	$	7,700	$	4,195
	Covenants not-to-compete (useful life of 4-6 years)		3,625		3,587		3,625		3,572
		$	11,325	$	8,382	$	11,325	$	7,767
Summary of Estimated Amortization Expense	Estimated amortization expense for the five succeeding years follows (in thousands):
		Amount
	2015	$	615
	2016		615
	2017		317
	2018		310
	2019		310
	Total	$	2,167

Computation_of_Earnings_Per_Sh1

Computation of Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2014
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):
		Years Ended December 31,
		2014		2013		2012
	Numerator:
	Net income	$	51,991	$	43,627	$	32,048
	Denominator:
	Denominator for basic earnings per share — weighted average common shares		24,505		24,154		23,823
	Effect of dilutive stock options		239		297		180
	Effect of other common stock equivalents		719		754		812
	Denominator for diluted earnings per share — adjusted weighted average common shares		25,463		25,205		24,815
	Basic Earnings Per Share	$	2.12	$	1.81	$	1.35
	Diluted Earnings Per Share	$	2.04	$	1.73	$	1.29

Stockholders_Equity_Tables

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2014
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:
		Years ended December 31,
		2014		2013		2012
	Shares of common stock purchased		1,400		5,900		13,650
	Aggregate purchase price of shares purchased	$	52,961	$	158,060	$	158,883
	Shares of common stock sold		9,729		11,719		14,882
	Aggregate sale price of shares sold	$	53,962	$	158,060	$	206,794

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Option Activity	The following table summarizes the activity of stock options for the year ended December 31, 2014 for both employees and non-employee directors:
		Options			Weighted			Weighted			Aggregate
					average			Average			Intrinsic
					exercise price			Remaining			Value
								Contractual			(000’s)
								Life (years)
	Outstanding at December 31, 2013		588,510		$	14.76
	Granted		116,240
	Exercised		(320,625	)
	Forfeited		(24,750	)
	Expired		—
	Outstanding at December 31, 2014		359,375		$	22.03			5.1		$	11,975
	Exercisable at December 31, 2014		—		$	—			—		$	—
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, 2014, 2013 and 2012:
		2014			2013			2012
	Risk free interest rate		1.58	%		0.8	%		0.84	%
	Expected life in years		4.5			4.5			5
	Expected volatility		44.33	%		58.5	%		59.82	%
	Dividend rate		—			—			—
Summary of Unvested Option	The following table summarizes the status of the Company’s unvested options as of December 31, 2014 and changes during the year ended December 31, 2014:
		Options			Weighted average
					Grant-date Fair  Value
	Unvested at December 31, 2013		429,810		$	8.02
	Granted		116,240			12.12
	Vested		(161,925	)		6.75
	Forfeited		(24,750	)		9.46
	Unvested at December 31, 2014		359,375		$	9.82
Summary of Restricted Stock Activity	The following table summarizes restricted stock activity during the year ended December 31, 2014:
		Shares			Weighted average
					Grant-date Fair  Value
	Restricted Stock at December 31, 2013		122,731		$	11
	Granted		7,936		$	50.4
	Vested		(15,152	)	$	11
	Forfeited		(7,576	)	$	11
	Restricted Stock at December 31, 2014		107,939		$	13.9

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
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):
		2014			2013
	Depreciation		100,607		$	88,522
	Other		(559	)		3,548
	Revenue		0			120
	Gross deferred tax liabilities		100,048			92,190
	Allowance for doubtful accounts		(1,511	)		(1,467	)
	Equity-based compensation		(3,440	)		(3,287	)
	Employee benefits		(7,024	)		(6,996	)
	Claims and insurance		(22,019	)		(19,374	)
	Other		(7,108	)		(11,571	)
	Gross deferred tax assets		(41,102	)		(42,695	)
	Net deferred tax liability	$	58,946		$	49,495
Summary of Income Tax Provision	The income tax provision for continuing operations consists of the following (in thousands):
		2014			2013			2012
	Current:
	U.S. federal	$	18,085		$	9,924		$	16,837
	State		1,690			2,496			2,959
	Total current income tax provision		19,775			12,420			19,796
	Deferred:
	U.S. federal		9,547			11,822			(678	)
	State		(85	)		276			(27	)
	Total deferred income tax (benefit) provision		9,462			12,098			(705	)
	Total income tax provision	$	29,237		$	24,518		$	19,091
Summary of Reconciliation Between Income Taxes and Effective Income Tax Provision	A reconciliation between income taxes at the federal statutory rate (35 percent) and the effective income tax provision is as follows:
		2014			2013			2012
	Provision at federal statutory rate	$	28,430		$	23,851		$	17,899
	State income taxes, net		2,426			2,574			2,025
	Nondeductible business expenses		589			675			503
	Tax credits		(1,434	)		(2,429	)		(253	)
	Other, net		(774	)		(153	)		(1,083	)
	Total provision	$	29,237		$	24,518		$	19,091
Summary of Gross Unrecognized Tax Benefits	A reconciliation of the beginning and ending total amounts of gross unrecognized tax benefits is as follows:
		2014			2013
	Gross unrecognized tax benefits at beginning of year	$	1,281		$	1,290
	Gross decreases in tax positions for prior years		—			—
	Gross increases in tax positions for current year		202			—
	Settlements		—			—
	Lapse of statute of limitations		(318	)		(9	)
	Gross unrecognized tax benefits at end of year	$	1,165		$	1,281

Summary_of_Quarterly_Operating1

Summary of Quarterly Operating Results (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Operating Results (Unaudited)	(Amounts in thousands, except per share data)
	Three months ended, 2014	March 31		June 30		September 30		December 31
	Operating revenue	$	299,730	$	330,399	$	332,544	$	309,648
	Operating income		15,231		22,741		27,149		20,572
	Net income		8,576		13,568		16,278		13,569
	Basic earnings per share	$	0.35	$	0.55	$	0.66	$	0.55
	Diluted earnings per share	$	0.34	$	0.53	$	0.64	$	0.53
	Three months ended, 2013	31-Mar		30-Jun		30-Sep		31-Dec
	Operating revenue	$	273,795	$	292,557	$	293,087	$	279,655
	Operating income		14,532		23,259		21,935		14,692
	Net income		9,155		13,500		12,908		8,064
	Basic earnings per share	$	0.38	$	0.56	$	0.53	$	0.33
	Diluted earnings per share	$	0.37	$	0.54	$	0.51	$	0.32

Acquisition_Tables

Acquisition (Tables)	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Summary of Cash Purchase Price Allocated Based on Independent Appraisals and Managements Estimates	The cash purchase price has been allocated based on independent appraisals and management’s estimates as follows (in thousands):
	Consideration:
	Cash	$	(7,934	)
	Contingent consideration arrangement		(1,162	)
	Fair value of total consideration transferred	$	(9,096	)
	Acquisition related costs included in SG&A		150
	Recognized amounts of identifiable assets acquired and liabilities assumed:
	Current assets	$	2,082
	Property and equipment		44
	Customer lists		3,184
	Current liabilities		(1,445	)
	Total identifiable net assets assumed	$	3,865
	Goodwill		5,231
	Total	$	9,096

Valuation_and_Qualifying_Accou1

Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2014
Valuation and Qualifying Accounts [Abstract]
Summary of Valuation and Qualifying Accounts	For the Years Ended December 31, 2014, 2013 and 2012
	(in thousands)
					Additions
	Description		Balance,		Charged to		Charged		Deductions-(1)			Balance,
			beginning		costs and		to other					end of
			of period		expenses		accounts					period
	Year ended December 31, 2014:
	Deducted from asset account – Allowance for uncollectible accounts		$	3,737	$	1,942		—	($	1,811	)	$	3,868
	Year ended December 31, 2013:
	Deducted from asset account – Allowance for uncollectible accounts			3,881		2,227		—		(2,371	)		3,737
	Year ended December 31, 2012:
	Deducted from asset account – Allowance for uncollectible accounts			3,811		1,833		—		(1,763	)		3,881
	-1	Primarily uncollectible accounts written off — net of recoveries.

Description_of_Business_and_Su3

Description of Business and Summary of Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	16-May-13
	Customer
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Common stock dividend				50.00%
Common stock split	Three-for-two
Depreciation	$58.40	$51	$47.50
Primary payroll-related costs capitalized	1	2.1	1
Stock-based awards compensation expense amortization period	3 years
Number of customers	0
Percentage of consolidated operating revenue	6.00%
Advertising costs	$1.90	$0.80	$0.70

Description_of_Business_and_Su4

Description of Business and Summary of Accounting Policies - Summary of Property and Equipment, Estimated Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2014
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	8 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	10 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_Su5

Description of Business and Summary of Accounting Policies - Schedule of Property and Equipment (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$891,145	$797,527
Land [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	53,632	52,745
Structures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	140,206	115,874
Tractors [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	290,717	273,129
Trailers [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	237,262	202,173
Other Revenue Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	37,220	34,616
Technology Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	63,773	58,957
Other [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$68,334	$60,033

Description_of_Business_and_Su6

Description of Business and Summary of Accounting Policies - Summary of Risk Retention Amounts Per Occurrence (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
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	350,000
Cargo loss and damage	$250,000

Debt_and_Financing_Arrangement2

Debt and Financing Arrangements - Summary of Reconciliation of Debt (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Debt Disclosure [Line Items]
Capital Leases, described below	$16,606
Total debt	83,035	76,883
Less: current portion of long-term debt	9,138	7,143
Long-term debt, less current portion	73,897	69,740
Credit Agreement with Banks [Member]
Debt Disclosure [Line Items]
Total debt	45,000	48,312
Senior Notes under Master Shelf Agreement [Member]
Debt Disclosure [Line Items]
Total debt	$21,429	$28,571

Debt_and_Financing_Arrangement3

Debt and Financing Arrangements - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2008	Nov. 30, 2007	Apr. 30, 2005	Sep. 20, 2002
Line of Credit Facility [Line Items]
Amendment line of credit facility expiration year and month	2018-06
Letter of credit facility outstanding amount	$47,300,000	$59,100,000
Total debt	83,035,000	76,883,000
Capital lease obligation	16,606,000
Lease expiration period	7 years
Weighted average interest rate for capital lease	2.92%
Cash paid for interest	4,500,000	6,100,000	7,300,000
Estimated fair value of total debt	83,700,000	78,000,000
Minimum [Member]
Line of Credit Facility [Line Items]
Letter of credit fee	1.38%
Letter of credit unused portion fee	0.20%
Maximum [Member]
Line of Credit Facility [Line Items]
Letter of credit fee	2.63%
Letter of credit unused portion fee	0.33%
LIBOR Rate Margin [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Rate margin	1.25%
Senior Notes under Master Shelf Agreement [Member]
Line of Credit Facility [Line Items]
Total debt	21,429,000	28,571,000
Senior notes issued, value				25,000,000	25,000,000		100,000,000
Senior notes authorized amount						150,000,000	125,000,000
Interest rate on notes				6.17%	6.14%		7.38%
Senior credit facility, Interest rate terms description	The initial $100 million Senior Notes had a fixed interest rate of 7.38 percent. Payments due under the $100 million Senior Notes were interest only until June 30, 2006 and at that time semi-annual principal payments began with the final payment made in December 2013. The November 2007 issuance of $25 million Senior Notes has a fixed interest rate of 6.14 percent. The January 2008 issuance of $25 million Senior Notes has a fixed interest rate of 6.17 percent. Payments due for both $25 million issuances were interest only until June 30, 2011 and at that time semi-annual principal payments began with the final payments due January 1, 2018.
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Borrowing capacity under credit agreement	200,000,000
Line of credit facility expiration year and month	2018-06
Additional borrowing capacity under revolving credit facility	40,000,000
Credit Agreement with Banks [Member]
Line of Credit Facility [Line Items]
Total debt	$45,000,000	$48,312,000
Credit Agreement with Banks [Member] | LIBOR Rate Margin [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Rate margin	2.50%
Credit Agreement with Banks [Member] | Base Rate Margin [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Rate margin	0.13%
Credit Agreement with Banks [Member] | Base Rate Margin [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Rate margin	0.50%

Debt_and_Financing_Arrangement4

Debt and Financing Arrangements - Schedule of Principal Maturities of Long-Term Debt (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Debt Disclosure [Abstract]
2015	$9,504
2016	9,596
2017	9,596
2018	47,453
2019	2,453
Thereafter	6,330
Total Payments	84,932
Less: Amounts Representing Interest on Capital Leases	1,897
Total	$83,035

Commitments_Contingencies_and_2

Commitments, Contingencies and Uncertainties - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$17.10	$17.90	$17.70
Capital expenditures committed	74.4
Capital expenditures in accounts payable	$1.80	$1.60

Commitments_Contingencies_and_3

Commitments, Contingencies and Uncertainties - Schedule of Non-Cancellable Capital and Operating Lease Agreements Requiring Minimum Annual Rentals Payable (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
2015	$14,051
2016	11,215
2017	9,780
2018	7,460
2019	5,291
Thereafter	12,778
Total	$60,575

Goodwill_and_Other_Intangible_2

Goodwill and Other Intangible Assets - Summary of Changes in Gross Carrying Amounts of Goodwill (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$5,231	$5,231
No Activity	0	0
Goodwill, Ending Balance	$5,231	$5,231

Goodwill_and_Other_Intangible_3

Goodwill and Other Intangible Assets - Summary of Gross Amounts and Accumulated Amortization of Identifiable Intangible Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$11,325	$11,325
Accumulated Amortization	8,382	7,767
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Amount	7,700	7,700
Accumulated Amortization	4,795	4,195
Covenants not-to-Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Amount	3,625	3,625
Accumulated Amortization	$3,587	$3,572

Goodwill_and_Other_Intangible_4

Goodwill and Other Intangible Assets - Summary of Gross Amounts and Accumulated Amortization of Identifiable Intangible Assets (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2014
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	10 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_5

Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense for intangible assets	$0.60	$0.60	$0.50

Goodwill_and_Other_Intangible_6

Goodwill and Other Intangible Assets - Summary of Estimated Amortization Expense (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2015	$615
2016	615
2017	317
2018	310
2019	310
Total	$2,167

Computation_of_Earnings_Per_Sh2

Computation of Earnings Per Share - Summary of Calculation of Basic Earnings Per Common Share and Diluted Earnings Per Common Share (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income	$13,569	$16,278	$13,568	$8,576	$8,064	$12,908	$13,500	$9,155	$51,991	$43,627	$32,048
Denominator:
Denominator for basic earnings per share - weighted average common shares									24,505	24,154	23,823
Effect of dilutive stock options									239	297	180
Effect of other common stock equivalents									719	754	812
Denominator for diluted earnings per share - adjusted weighted average common shares									25,463	25,205	24,815
Basic Earnings Per Share	$0.55	$0.66	$0.55	$0.35	$0.33	$0.53	$0.56	$0.38	$2.12	$1.81	$1.35
Diluted Earnings Per Share	$0.53	$0.64	$0.53	$0.34	$0.32	$0.51	$0.54	$0.37	$2.04	$1.73	$1.29

Computation_of_Earnings_Per_Sh3

Computation of Earnings Per Share - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Common stock excluded from the calculation of diluted earnings per share	7,936	143,640

Stockholders_Equity_Summary_of

Stockholders' Equity - Summary of Purchase and Sale of Common Stock (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Shares of common stock purchased	1,400	5,900	13,650
Aggregate purchase price of shares purchased	$52,961	$158,060	$158,883
Shares of common stock sold	9,729	11,719	14,882
Aggregate sale price of shares sold	$53,962	$158,060	$206,794

Stockholders_Equity_Additional

Stockholders' Equity - Additional Information (Detail)	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Shares reserved for issuance under the Directors Deferred Fee Plan	244,835	228,546

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in cash flows from financing activities	$4	$2.10	$0.10
Non-employee director stock options plan expiration period	10 years
Stock option and restricted stock compensation expense	2.2	1.2	1.1
Unrecognized compensation expense	2.2
Weighted average recognition period of compensation expenses	2 years 1 month 6 days
Total intrinsic value of options exercised	9.9	4.7	0.4
Weighted-average grant-date fair value per share of options granted	$12.12	$12.95	$5.57
Weighted-average grant-date fair value per share of shares vested	$6.75	$4.15	$4.25
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares awarded, other than options granted in period	7,936
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	3 years
Operating expense	$1.20	$1	$1
After three years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting percentage	25.00%
After three years [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	3 years
After four years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting percentage	25.00%
After four years [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	4 years
After five years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting percentage	50.00%
After five years [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vesting period	5 years
February 2011 - February 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range				106,330
2010-2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range					150,384
2012 - 2014 [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range						146,052
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range	68,200
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period share issuance range	0
Non Employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual service	3 years
Contractual term	7 years
Exercisable period month after date of grant	6 months
Shares issued to non employee director	1,905	2,199	4,063
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
Last date till the share can be granted	22-Jan-13
Reserved and unissued shares	0	158,700
2011 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved	2,025,000
Restricted stock vesting period	3 years
Reserved and unissued shares	1,257,996
2011 Omnibus Incentive Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares awarded, other than options granted in period	7,936
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
Directors' Deferred Fee Plan [Member] | Non Employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units issued to non employee directors	16,561	24,191	40,398
2003 Omnibus incentive plan and 2011 Omnibus incentive plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum member of management and executive employees eligible for awards	20

StockBased_Compensation_Summar

Stock-Based Compensation - Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Beginning balance, options	588,510
Granted, options	116,240
Exercised, options	-320,625
Forfeited, options	-24,750
Expired, options	0
Ending balance, options	359,375
Exercisable options, ending balance	0
Beginning balance, weighted average exercise price	$14.76
Ending balance, weighted average exercise price	$22.03
Exercisable, weighted average exercisable price	$0
Outstanding, weighted average remaining contractual life (years)	5 years 1 month 6 days
Exercisable, weighted average remaining contractual life (years)	0 years
Outstanding, aggregate intrinsic value	$11,975
Exercisable, aggregate intrinsic value	$0

StockBased_Compensation_Summar1

Stock-Based Compensation - Summary of Weighted Average Assumptions Used In Valuing Options (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk free interest rate	1.58%	0.80%	0.84%
Expected life in years	4 years 6 months	4 years 6 months	5 years
Expected volatility	44.33%	58.50%	59.82%
Dividend rate	0.00%	0.00%	0.00%

StockBased_Compensation_Summar2

Stock-Based Compensation - Summary of Unvested Option (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Unvested, options beginning balance	429,810
Granted, options	116,240
Vested, options	-161,925
Forfeited, options	-24,750
Unvested, options ending balance	359,375	429,810
Unvested , weighted average grant date fair value beginning balance	$8.02
Granted, weighted average grant date fair value	$12.12	$12.95	$5.57
Vested, weighted average grant date fair value	$6.75
Forfeited, weighted average grant date fair value	$9.46
Unvested , weighted average grant date fair value ending balance	$9.82	$8.02

StockBased_Compensation_Summar3

Stock-Based Compensation - Summary of Restricted Stock Activity (Detail) (Restricted Stock [Member], USD $)	12 Months Ended
	Dec. 31, 2014
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, options beginning balance	122,731
Granted, options	7,936
Vested, options	-15,152
Forfeited, options	-7,576
Unvested, options ending balance	107,939
Unvested , weighted average grant date fair value beginning balance	$11
Granted	$50.40
Vested	$11
Forfeited	$11
Unvested , weighted average grant date fair value ending balance	$13.90

Employee_Benefits_Additional_I

Employee Benefits - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
In Millions, except Share data, unless otherwise specified	Apr. 30, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Reinstatement of contribution matching percentage	50.00%
Contribution in operation		$5.70	$2.50	$2.10
Shares held by the Rabbi trust		193,607	201,936
Performance incentive accruals		$6.50	$8.80	$8.40
Payroll deduction for ESPP, percent of annual wages		10.00%
Shares purchased by custodians		4,751	6,711	13,830
401(k)Saving Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Company match of contribution		50.00%
Employees contribution share		6.00%

Income_Taxes_Summary_of_Deferr

Income Taxes - Summary of Deferred Tax Liabilities and Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Income Tax Disclosure [Abstract]
Depreciation	$100,607	$88,522
Other	-559	3,548
Revenue	0	120
Gross deferred tax liabilities	100,048	92,190
Allowance for doubtful accounts	-1,511	-1,467
Equity-based compensation	-3,440	-3,287
Employee benefits	-7,024	-6,996
Claims and insurance	-22,019	-19,374
Other	-7,108	-11,571
Gross deferred tax assets	-41,102	-42,695
Net deferred tax liability	$58,946	$49,495

Income_Taxes_Summary_of_Income

Income Taxes - Summary of Income Tax Provision (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current:
U.S. federal	$18,085	$9,924	$16,837
State	1,690	2,496	2,959
Total current income tax provision	19,775	12,420	19,796
Deferred:
U.S. federal	9,547	11,822	-678
State	-85	276	-27
Total deferred income tax (benefit) provision	9,462	12,098	-705
Total income tax provision	$29,237	$24,518	$19,091

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2013
Income Tax [Line Items]
Federal statutory income tax rate	35.00%
Interest related to unrecognized tax benefits	$0.30	$0.10	$0.10
Accrued interest and penalties related to unrecognized tax benefits	1.3	1.6	1.4
Unrecognized tax benefits that would affect the Company's effective tax rate if recognized	1.2	1.3
Cash (received) paid for income taxes	20.8	20.6	19.3
Tax credit recognized in first quarter of 2013				$1
Maximum [Member]
Income Tax [Line Items]
Income tax year open for examination	2014
Maximum [Member] | State and Local Jurisdiction [Member]
Income Tax [Line Items]
Income tax year open for examination	2013
Minimum [Member]
Income Tax [Line Items]
Income tax year open for examination	2012
Minimum [Member] | State and Local Jurisdiction [Member]
Income Tax [Line Items]
Income tax year open for examination	2005

Income_Taxes_Summary_of_Reconc

Income Taxes - Summary of Reconciliation Between Income Taxes and Effective Income Tax Provision (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Provision at federal statutory rate, taxable amount	$28,430	$23,851	$17,899
State income taxes, net	2,426	2,574	2,025
Nondeductible business expenses	589	675	503
Tax credits	-1,434	-2,429	-253
Other, net	-774	-153	-1,083
Total income tax provision	$29,237	$24,518	$19,091

Income_Taxes_Summary_of_Gross_

Income Taxes - Summary of Gross Unrecognized Tax Benefits (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits at beginning of year	$1,281	$1,290
Gross decreases in tax positions for prior years	0	0
Gross increases in tax positions for current year	202
Settlements	0	0
Lapse of statute of limitations	-318	-9
Gross unrecognized tax benefits at end of year	$1,165	$1,281

Summary_of_Quarterly_Operating2

Summary of Quarterly Operating Results (Unaudited) - Summary of Quarterly Operating Results (Unaudited) (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Operating Revenue	$309,648	$332,544	$330,399	$299,730	$279,655	$293,087	$292,557	$273,795	$1,272,321	$1,139,094	$1,098,679
Operating income	20,572	27,149	22,741	15,231	14,692	21,935	23,259	14,532	85,693	74,418	58,734
Net income	$13,569	$16,278	$13,568	$8,576	$8,064	$12,908	$13,500	$9,155	$51,991	$43,627	$32,048
Basic Earnings Per Share	$0.55	$0.66	$0.55	$0.35	$0.33	$0.53	$0.56	$0.38	$2.12	$1.81	$1.35
Diluted Earnings Per Share	$0.53	$0.64	$0.53	$0.34	$0.32	$0.51	$0.54	$0.37	$2.04	$1.73	$1.29

Acquisition_Additional_Informa

Acquisition - Additional Information (Detail) (USD $)	1 Months Ended
In Millions, unless otherwise specified	Feb. 28, 2014	Jul. 02, 2012
Business Acquisition [Line Items]
Purchase price of acquisition		$7.90
Purchase price of acquisition excluding cash acquired		7.6
Purchase price of acquisition cash acquired value		0.3
Maximum [Member]
Business Acquisition [Line Items]
Maximum earnout subject to performance of acquired companies in 2013		1.3
Maximum earnout paid subject to performance of acquired companies in 2013	$1.30

Acquisition_Summary_of_Cash_Pu

Acquisition - Summary of Cash Purchase Price Allocated Based on Independent Appraisals and Managements Estimates (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Recognized amounts of identifiable assets acquired and liabilities assumed:
Goodwill		$5,231	$5,231	$5,231
Robart Transportation Inc [Member]
Consideration:
Cash	-7,934
Contingent consideration arrangement	-1,162
Fair value of total consideration transferred	-9,096
Acquisition related costs included in SG&A	150
Recognized amounts of identifiable assets acquired and liabilities assumed:
Current assets	2,082
Property and equipment	44
Customer lists	3,184
Current liabilities	-1,445
Total identifiable net assets assumed	3,865
Goodwill	5,231
Total	$9,096

RelatedParty_Transactions_Addi

Related-Party Transactions - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Yellow Corporation completed spin-off on September 30.2002	100.00%
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Letters of Credit	$1.80	$1.60
Cost plus basis points	1.25%

Valuation_and_Qualifying_Accou2

Valuation and Qualifying Accounts - Summary of Valuation and Qualifying Accounts (Detail) (Allowance for Uncollectible Accounts [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for Uncollectible Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance, beginning of period	$3,737	$3,881	$3,811
Additions - Charged to costs and expenses	1,942	2,227	1,833
Additions - Charged to other accounts	0	0	0
Deductions	-1,811	-2,371	-1,763
Balance, end of period	$3,868	$3,737	$3,881

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (Subsequent Event [Member], USD $)	0 Months Ended
In Thousands, unless otherwise specified	Feb. 02, 2015
Subsequent Event [Member]
Subsequent Event [Line Items]
Purchase price of acquisition	$25,000