Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements include the accounts of Saia, Inc. and its wholly-owned subsidiaries (together, the Company or Saia). All significant intercompany accounts and transactions have been eliminated in the condensed consolidated financial statements. The condensed consolidated financial statements have been prepared by the Company without audit by the independent registered public accounting firm. In the opinion of management, all normal recurring adjustments necessary for a fair presentation of the condensed consolidated balance sheets, statements of operations and cash flows for the interim periods included herein have been made. These interim condensed consolidated financial statements of the Company have been prepared in accordance with U.S. generally accepted accounting principles for interim financial information, the instructions to Quarterly Report on Form 10-Q and Rule 10-01 of Regulation S-X. Certain information and note disclosures normally included in financial statements prepared in accordance with U.S. generally accepted accounting principles have been condensed or omitted from these statements. The accompanying condensed consolidated financial statements should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2016. Operating results for the quarter ended March 31, 2017 are not necessarily indicative of the results of operations that may be expected for the year ended December 31, 2017.
Business	Business The Company provides regional and interregional less-than-truckload (LTL) services through a single integrated organization. While more than 99% of its revenue historically has been derived from transporting LTL shipments across 34 states, the Company also offers customers a wide range of other value-added services, including non-asset truckload, expedited and logistics services across the United States.
Other Current Liabilities	Other Current Liabilities Other current liabilities includes $33.4 million of claims and insurance liabilities as of March 31, 2017 and $33.0 million as of December 31, 2016.
Accounting Pronouncements Adopted in 2017	Accounting Pronouncements Adopted in 2017 In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting. The Company adopted this new standard effective January 1, 2017. As a result of adoption, $1.1 million of excess tax benefits related to share-based payments was recorded as an offset to income tax expense in the first quarter of 2017, as opposed to additional paid-in capital, and the windfall tax benefit was removed from the Company’s diluted shares calculation. The Company classified the $1.1 million of excess tax benefits related to share-based payments as operating activities, instead of financing activities, on the Condensed Consolidated Statements of Cash Flows for the first quarter of 2017. The Company elected to continue to use an estimated forfeiture rate for recording stock compensation expense and to withhold taxes at the minimum statutory rates. The Company classified $1.2 million in shares withheld for taxes as financing activities for the first quarter of 2017. Additionally, the Company reclassified $0.7 million in shares withheld for taxes from operating activities to financing activities for the first quarter of 2016. The Company had no other items requiring retrospective treatment under the pronouncement.
Accounting Pronouncements Not Yet Adopted	Accounting Pronouncements Not Yet Adopted In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“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. In July 2015, the FASB updated ASU No. 2014-09 to defer the effective date by one year. The new standard is effective for the Company on January 1, 2018, at which point the Company plans to adopt this standard. The standard permits the use of either the retrospective or cumulative effect transition method. The Company is evaluating the effect that ASU No. 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. While the Company has adopted a timeline for implementation and identified its revenue streams and contracts subject to the standard, the Company has not yet completed its evaluation of these. The Company is still in the process of evaluating its non-asset truckload and logistics business for gross versus net revenue presentation and the revenue recognition timing related to these services on the Condensed Consolidated Statements of Operations. However, the Company does not anticipate a significant change to other areas of its business. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), a leasing standard for both lessees and lessors. Under its core principle, a lessee will recognize lease assets and liabilities on the balance sheet for all arrangements with terms longer than 12 months. Lessor accounting remains largely consistent with existing U.S. generally accepted accounting principles. The new standard is effective for the Company on January 1, 2019. Early adoption is permitted. The standard requires the use of a modified retrospective transition method. The Company is evaluating the effect that ASU No. 2016-02 will have on its consolidated financial statements and related disclosures. While the Company has not completed its evaluation of the effect of the standard on its ongoing financial reporting, it believes the most significant changes relate to the recognition of lease assets and liabilities on its balance sheet.