Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2017
Summary of Significant Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation. The consolidated financial statements include the accounts of Kirby Corporation and all majority-owned subsidiaries (“the Company”). All investments in which the Company owns 20% to 50% and exercises significant influence over operating and financial policies are accounted for using the equity method. All material intercompany accounts and transactions have been eliminated in consolidation. Certain reclassifications have been made to reflect the current presentation of financial information.
Cash Equivalents	Cash Equivalents. Cash equivalents consist of all short-term, highly liquid investments with maturities of three months or less at date of purchase.
Accounts Receivable	Accounts Receivable. In the normal course of business, the Company extends credit to its customers. The Company regularly reviews the accounts and makes adequate provisions for probable uncollectible balances. It is the Company’s opinion that the accounts have no impairment, other than that for which provisions have been made. Included in accounts receivable as of December 31, 2017 and 2016 were $153,661,000 and $84,453,000, respectively, of accruals for revenues earned which have not been invoiced as of the end of each year. The Company’s marine transportation and distribution and services operations are subject to hazards associated with such businesses. The Company maintains insurance coverage against these hazards with insurance companies. Included in accounts receivable as of December 31, 2017 and 2016 were $66,588,000 and $88,182,000, respectively, of receivables from insurance companies to cover claims in excess of the Company’s deductible.
Concentrations of Credit Risk	Concentrations of Credit Risk. Financial instruments which potentially subject the Company to concentrations of credit risk are primarily trade accounts receivables. The Company’s marine transportation customers include the major oil refining and petrochemical companies. The distribution and services customers are oilfield service companies, oil and gas operators and producers, on-highway transportation companies, marine transportation companies, commercial fishing companies, construction companies, mining companies, power generation companies, and the United States government. The Company regularly reviews its accounts and estimates the amount of uncollectible receivables each period and establishes an allowance for uncollectible amounts. The amount of the allowance is based on the age of unpaid amounts, information about the current financial strength of customers, and other relevant information. Estimates of uncollectible amounts are revised each period, and changes are recorded in the period they become known.
Fair Value of Financial Instruments	Fair Value of Financial Instruments. Cash, accounts receivable, accounts payable and accrued liabilities have carrying values that approximate fair value due to the short-term maturity of these financial instruments. The fair value of the Company’s debt instruments is more fully described in Note 6, Long-Term Debt.
Property, Maintenance and Repairs	Property, Maintenance and Repairs. Property is recorded at cost. Improvements and betterments are capitalized as incurred. Depreciation is recorded on the straight-line method over the estimated useful lives of the individual assets as follows: marine transportation equipment, 5-40 years; buildings, 10-40 years; other equipment, 2-10 years; and leasehold improvements, term of lease. When property items are retired, sold or otherwise disposed of, the related cost and accumulated depreciation are removed from the accounts with any gain or loss on the disposition included in the statement of earnings. Maintenance and repairs on vessels built for use on the inland waterways are charged to operating expense as incurred and includes the costs incurred in United States Coast Guard (“USCG”) inspections unless the shipyard extends the life or improves the operating capacity of the vessel which results in the costs being capitalized.
Drydocking on Ocean-Going Vessels	Drydocking on Ocean-Going Vessels. The Company’s ocean-going vessels are subject to regulatory drydocking requirements after certain periods of time to be inspected, have planned major maintenance performed and be recertified by the American Bureau of Shipping (“ABS”). These recertifications generally occur twice in a five year period. The Company defers the drydocking expenditures incurred on its ocean-going vessels due to regulatory marine inspections by the ABS and amortizes the costs of the shipyard over the period between drydockings, generally 30 or 60 months, depending on the type of major maintenance performed. Drydocking expenditures that extend the life or improve the operating capability of the vessel result in the costs being capitalized. The Company recognized amortization of major maintenance costs of $21,207,000, $19,869,000 and $22,126,000 for the years ended December 31, 2017, 2016 and 2015, respectively, in costs of sales and operating expenses. Routine repairs and maintenance on ocean-going vessels are expensed as incurred. Interest is capitalized on the construction of new ocean-going vessels. Interest expense excludes capitalized interest of $1,731,000, $2,974,000 and $3,026,000 for the years ending December 31, 2017, 2016 and 2015, respectively.
Environmental Liabilities	Environmental Liabilities. The Company expenses costs related to environmental events as they are incurred or when a loss is considered probable and estimable.
Goodwill	Goodwill. The excess of the purchase price over the fair value of identifiable net assets acquired in transactions accounted for as a purchase is included in goodwill. The Company conducted its annual goodwill impairment test at November 30, 2017 and 2016. For 2017 and 2016, the Company noted no impairment of goodwill. The Company will continue to conduct goodwill impairment tests as of November 30 of subsequent years, or whenever events or circumstances indicate that interim impairment testing is necessary. The amount of goodwill impairment, if any, is typically measured based on projected discounted future operating cash flows using an appropriate discount rate. The gross carrying value of goodwill at December 31, 2017 and 2016 was $947,502,000 and $615,598,000, respectively, and accumulated amortization at December 31, 2017 and 2016 was $15,566,000. Accumulated impairment losses were $1,901,000 at December 31, 2017 and 2016. Net goodwill for the marine transportation segment was $387,504,000 and $382,227,000 at December 31, 2017 and 2016, respectively. The increase in net goodwill for the marine transportation segment for 2017 was due to the purchase of a barge fleeting and marine fueling operation, as well as San Jac Marine, LLC (“San Jac”), which are more fully described in Note 2, Acquisitions. Net goodwill for the distribution and services segment was $547,631,000 and $215,904,000 at December 31, 2017 and 2016, respectively. The increase in net goodwill for the distribution and services segment was due to the acquisition of Stewart & Stevenson LLC (“S&S”) in 2017, also more fully described in Note 2, Acquisitions.
Other Intangibles	Other Intangibles. Other intangibles include assets for customer contracts and relationships, distributorship and dealership agreements, trade names and noncompete agreements and liabilities for unfavorable leases. As of December 31, 2017 and 2016, the gross carrying amounts of other intangible assets were $315,983,000 and $158,634,000, respectively, and the accumulated amortization was $83,175,000 and $71,328,000, respectively, resulting in net carrying amounts of $232,808,000 and $87,306,000, respectively. As of December 31, 2017 and 2016, the gross carrying amounts of other intangible liabilities were $7,437,000 and $5,759,000, respectively, and the accumulated amortization was $4,751,000 and $3,949,000, respectively, resulting in net carrying amounts of $2,686,000 and $1,810,000, respectively. The costs of intangible assets and liabilities are amortized to expense in a systematic and rational manner over their estimated useful lives. For the years ended December 31, 2017, 2016 and 2015, the amortization expense for intangibles was $11,296,000, $8,467,000 and $8,526,000, respectively. Estimated amortization expense for amortizable intangible assets and liabilities for the next five years (2018 – 2022) is approximately $17,760,000, $17,395,000, $17,617,000, $17,171,000 and $16,971,000, respectively. As of December 31, 2017, the weighted average amortization period for intangible assets and liabilities was approximately 15 years.
Revenue Recognition	Revenue Recognition. The majority of marine transportation revenue is derived from term contracts, ranging from one to five years, some of which have renewal options, and the remainder is from spot market movements. The majority of the term contracts are for terms of one year. The Company is a provider of marine transportation services for its customers and, in almost all cases, does not assume ownership of the products it transports. A term contract is an agreement with a specific customer to transport cargo from a designated origin to a designated destination at a set rate or at a daily rate. The rate may or may not escalate during the term of the contract, however, the base rate generally remains constant and contracts often include escalation provisions to recover changes in specific costs such as fuel. A spot contract is an agreement with a customer to move cargo from a specific origin to a designated destination for a rate negotiated at the time the cargo movement takes place. Spot contract rates are at the current “market” rate, including fuel, and are subject to market volatility. The Company uses a voyage accounting method of revenue recognition for its marine transportation revenues which allocates voyage revenue based on the percent of the voyage completed during the period. There is no difference in the recognition of revenue between a term contract and a spot contract. Distribution products and services are generally sold based upon purchase orders or preferential service agreements with the customer that include fixed or determinable prices and that do not include right of return or significant post-delivery performance obligations. Parts sales are recognized when title passes upon shipment to customers or when customer-specific acceptance requirements are met. Service revenue is recognized as the service is provided. Revenue from rental agreements is recognized on a straight-line basis over the rental period. Distribution and services manufacturing and assembly projects revenue is reported on the percentage of completion method of accounting using measurements of progress towards completion appropriate for the work performed.
Stock-Based Compensation	Stock-Based Compensation. The Company has share-based compensation plans covering selected officers and other key employees as well as the Company’s Board of Directors. Stock-based grants made under the Company’s stock plans are recorded at fair value on the date of the grant and the cost is recognized ratably over the vesting period of the stock option or restricted stock. Stock option grants are valued at the date of grant as calculated under the Black-Scholes option pricing model. The Company’s stock-based compensation plans are more fully described in Note 9, Stock Award Plans.
Taxes on Income	Taxes on Income. The Company follows the asset and liability method of accounting for income taxes. 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 basis and operating loss and tax credit carryforwards. 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.
Accrued Insurance	Accrued Insurance. Accrued insurance liabilities include estimates based on individual incurred claims outstanding and an estimated amount for losses incurred but not reported (“IBNR”) or fully developed based on past experience. Insurance premiums, IBNR losses and incurred claim losses, in excess of the Company’s deductible for 2017, 2016 and 2015 were $26,195,000, $23,085,000 and $23,737,000, respectively.
Noncontrolling Interests	Noncontrolling Interests. The Company has a majority interest in and is the general partner in several affiliated entities. In situations where losses applicable to the minority interest in the affiliated entities exceed the limited partners’ equity capital, such excess and any further loss attributable to the minority interest is charged against the Company’s interest in the affiliated entities. If future earnings materialize in the respective affiliated entities, the Company’s interest would be credited to the extent of any losses previously absorbed.
Treasury Stock	Treasury Stock. The Company follows the average cost method of accounting for treasury stock transactions.
Impairment of Long-Lived Assets and for Long-Lived Assets to Be Disposed Of	Impairment of Long-lived Assets and for Long-lived Assets to Be Disposed Of. The Company reviews long-lived assets and certain identifiable intangibles for impairment by vessel class whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. Recoverability on marine transportation assets is assessed based on vessel classes, not on individual assets, because identifiable cash flows for individual marine transportation assets are not available. Projecting customer contract volumes allows estimation of future cash flows by projecting pricing and utilization by vessel class but it is not practical to project which individual marine transportation asset will be utilized for any given contract. Because customers do not specify which particular vessel is used, prices are quoted based on vessel classes not individual assets. Nominations of vessels for specific jobs are determined on a day by day basis and are a function of the equipment class required and the geographic position of vessels within that class at that particular time as vessels within a class are interchangeable and provide the same service. The Company’s vessels are mobile assets and equipped to operate in geographic regions throughout the United States and the Company has in the past and expects to continue to move vessels from one region to another when it is necessary due to changing markets and it is economical to do so. Barge vessel classes are based on similar capacities, hull type, and type of product and towing vessels are based on similar hull type and horsepower. Recoverability of the vessel classes is measured by a comparison of the carrying amount of the assets to future net cash flows expected to be generated by the assets. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the fair value of the assets. Assets to be disposed of are reported at the lower of the carrying amount or fair value less costs to sell.
Accounting Standards	Accounting Standards In February 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-02, “Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the recent federal tax reform legislation. ASU 2018-02 eliminates the stranded tax effects resulting from the recent federal tax reform legislation and will improve the usefulness of information reported to financial statement users. The amendments in ASU 2018-02 will be applied either in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the recent federal tax reform legislation is recognized. ASU 2018-02 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted, including adoption in any interim period, for which financial statements have not yet been made available for issuance. The Company is currently evaluating the impact, if any, that the adoption of this standard will have on its consolidated financial statements. In March 2017, the FASB issued ASU 2017-07, “Compensation – Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost” (“ASU 2017-07”) which requires employers to include only the service cost component of net periodic pension cost and net periodic postretirement benefit cost in operating expenses. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The standard allows only the service cost component to be eligible for capitalization when applicable. ASU 2017-07 is effective for annual and interim periods beginning after December 15, 2017 with early adoption permitted. This standard shall be applied retrospectively for the presentation of the service cost component and the other components of net periodic pension cost and net periodic postretirement benefit cost in the income statement and prospectively for the capitalization of the service cost benefit in assets. The Company will adopt the provisions of ASU 2017-07 on January 1, 2018 and the Company does not expect the adoption of ASU 2017-07 to have a material impact on its consolidated financial statements. In January 2017, the FASB issued ASU 2017-04, “Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment” (“ASU 2017-04”) which simplifies the subsequent measurement of goodwill by eliminating Step 2 in the goodwill impairment test that required an entity to perform procedures to determine the fair value of its assets and liabilities at the testing date. An entity instead will perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying value and record an impairment charge based on the excess of a reporting unit’s carrying amount over its fair value. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. ASU 2017-04 will be applied prospectively and is effective for annual and interim goodwill impairment tests conducted in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment testing dates after January 1, 2017. The Company is currently evaluating the impact, if any, that the adoption of this standard will have on its consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” (“ASU 2016-15”) to create consistency in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. ASU 2016-15 is effective for annual and interim periods beginning after December 15, 2017. The Company will adopt the provisions of ASU 2016-15 on January 1, 2018 and the Company does not expect the adoption of ASU 2016-15 to have a material impact on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, “Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”) which simplifies several aspects of the accounting for share-based payment transactions, including income tax consequences, forfeitures, minimum statutory tax withholding requirements, classification as either equity or liabilities, and classification on the statement of cash flows. The Company adopted the provisions of ASU 2016-09 on January 1, 2017. ASU 2016-09 requires all excess tax benefits and tax deficiencies be recognized as income tax expense or benefit in the income statement, thus eliminating additional paid-in capital pools. The Company recognized a cumulative effect adjustment of $8,486,000 to retained earnings on a modified retrospective basis as of January 1, 2017 and will apply the new standard guidance prospectively to all excess tax benefits and tax deficiencies resulting from settlements after January 1, 2017. The standard also requires a policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur. The Company will elect to account for forfeitures when they occur. Also, the standard requires that excess tax benefits should be classified along with other income tax cash flows as an operating activity on the statement of cash flows, which differs from the Company’s historical classification of excess tax benefits as cash inflows from financing activities. The Company elected to apply this provision using the prospective transition method. Additionally, the standard requires cash paid by an employer when directly withholding shares for tax withholding purposes to be classified in the statement of cash flows as a financing activity, which differs from the Company’s previous method of classification of such cash payments as an operating activity. The Company applied this provision retrospectively and reclassified $1,756,000 and $2,975,000 during 2016 and 2015, respectively, which increased net cash provided by operating activities and net cash used in financing activities. In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842)” (“ASU 2016-02”) to increase transparency and comparability among organizations by requiring recognition of lease assets and lease liabilities on the balance sheet and disclosure of key information about leasing arrangements. ASU 2016-02 is effective for annual and interim periods beginning after December 15, 2018, with early adoption permitted. A modified retrospective approach is required. The Company has formed a project team to evaluate the impact that the adoption of this standard will have on its consolidated financial statements and disclosures. The project team has completed training on the new standard and has started lease review and documentation, but the Company has not yet determined the effect of ASU 2016-02 on its ongoing financial reporting. In November 2015, the FASB issued ASU 2015-17, “Balance Sheet Classification of Deferred Taxes” (“ASU 2015-17”) which requires that deferred tax liabilities and assets be classified as noncurrent on the balance sheet. The current requirement that deferred tax liabilities and assets of a tax-paying component of an entity be offset and presented as a single amount is not affected by this guidance. The guidance may be applied either prospectively to all deferred tax liabilities and assets or retrospectively to all periods presented. The Company adopted the provisions of ASU 2015-17 on January 1, 2017 on a retrospective basis. The December 31, 2016 current deferred tax assets of $13,604,000 have been reclassified in the consolidated balance sheet from current deferred income taxes asset to noncurrent deferred income taxes liability. In July 2015, the FASB issued ASU 2015-11, “Inventory (Topic 330): Simplifying the Measurement of Inventory” (“ASU 2015-11”) which applies to inventory that is measured using first-in, first-out (“FIFO”) or average cost. Under the guidance, an entity should measure inventory that is within the scope of this update at the lower of cost and net realizable value. Net realizable value is the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. ASU 2015-11 is effective for annual and interim periods beginning after December 15, 2016, and should be applied prospectively with early adoption permitted at the beginning of an interim period or annual reporting period. The Company adopted the provisions of ASU 2015-11 on January 1, 2017 and, based on a lower of cost and net realizable value inventory analysis as of December 31, 2016, no adjustments to inventory value were required. The analysis reflected the inventory values are proper within the guidance of ASU 2015-11. In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers” (“ASU 2014-09”). ASU 2014-09 requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU 2014-09 will replace most existing revenue recognition guidance in United States Generally Accepted Accounting Principles when it becomes effective. In July 2015, the FASB voted to delay the effective date of ASU 2014-09 by one year, making it effective for fiscal years, and interim periods within those years, beginning after December 15, 2017, with early adoption permitted as of the original effective date. ASU 2014-09 permits the use of either the retrospective, modified retrospective or prospective with a cumulative catch-up approach. The Company will adopt ASU 2014-09 on January 1, 2018 with a cumulative adjustment that will decrease retained earnings by approximately $10,000,000 rather than restating previously reported results. The cumulative adjustment will primarily relate to recognition of revenue on certain contract manufacturing activities, primarily construction of new pressure pumping units in the Company’s distribution and services segment. The Company currently recognizes revenue on manufacturing and assembly projects on a percentage of completion method using measurements of progress towards completion appropriate for the work performed. Upon the adoption of ASU 2014-09, the Company will recognize the revenues on contract manufacturing activities upon shipment and transfer of control versus the percentage of completion method.