75000 - Document - Document and Entity Information link:presentationLink link:calculationLink link:definitionLink 75010 - Statement - Statements of Net Assets Available for Benefits link:presentationLink link:calculationLink link:definitionLink 75020 - Statement - Statements of Changes in Net Assets Available for Benefits link:presentationLink link:calculationLink link:definitionLink 75030 - Disclosure - Description of Plan link:presentationLink link:calculationLink link:definitionLink 75040 - Disclosure - Summary of Significant Accounting Policies link:presentationLink link:calculationLink link:definitionLink 75050 - Disclosure - Investments and Investment Options link:presentationLink link:calculationLink link:definitionLink 75060 - Disclosure - Voting Rights link:presentationLink link:calculationLink link:definitionLink 75070 - Disclosure - Risk and Uncertainties link:presentationLink link:calculationLink link:definitionLink 75080 - Disclosure - Related Party Transactions link:presentationLink link:calculationLink link:definitionLink 75090 - Disclosure - Federal Income Tax Status link:presentationLink link:calculationLink link:definitionLink 75100 - Disclosure - Fair Value Measurements link:presentationLink link:calculationLink link:definitionLink 75110 - Disclosure - Schedule of Assets (Held at End of Year) link:presentationLink link:calculationLink link:definitionLink 75120 - Disclosure - Summary of Significant Accounting Policies (Policies) link:presentationLink link:calculationLink link:definitionLink 75130 - Disclosure - Fair Value Measurements (Tables) link:presentationLink link:calculationLink link:definitionLink 75140 - Disclosure - Schedule of Assets (Held at End of Year) (Tables) link:presentationLink link:calculationLink link:definitionLink 75150 - Disclosure - Description of Plan - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 75160 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 75170 - Disclosure - Federal Income Tax Status - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 75180 - Disclosure - Fair Value Measurements - Schedeule of Investments Measured at Fair Value on a Recurring Basis (Details) link:presentationLink link:calculationLink link:definitionLink 75190 - Disclosure - Schedule of Assets (Held at End of Year) (Details) link:presentationLink link:calculationLink link:definitionLink 75190 - Disclosure - Schedule of Assets (Held at End of Year) (Details) [Default] link:presentationLink link:calculationLink link:definitionLink Additions to net assets attributed to: EBP, Change in Net Asset Available for Benefit, Increase [Abstract] Benefits paid to participants EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant EBP, Related Party and Party-in-Interest Transactions [Line Items] Document Fiscal Period Focus Employee contributions remitted to trust EBP, Employer Contribution, Receivable EBP, Forfeited Nonvested Account, Decrease from Employer Contribution Forfeitures from non-vested accounts to reduce the Plan's matching contributions EBP, Tax Status [Abstract] EBP, Forfeited Nonvested Account Total forfeitures Description of Plan EBP, Description of Plan [Text Block] EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Note Receivable from Participant Interest income from participants' notes receivable Investment, Identifier [Axis] EBP, Description of Plan [Line Items] EBP, Employer Contribution, Matching Percentage Matching employer contribution EBP, Investment, Issuer Name [Extensible Enumeration] EBP, Investment, Fair Value and NAV [Abstract] Highly Compensated Employees [Member] Highly Compensated Employees. Highly Compensated Employees EBP, Accounting Policy [Line Items] Employee Benefit Plan, Additional Employer Discretionary Contribution, Percentage Additional employer discretionary contribution as a percentage of employee's considered compensation. Additional employer discretionary contribution percentage EBP, Schedule of Asset Held for Investment [Table] EBP, Statement of Net Asset Available for Benefit [Line Items] Receivable from participants, maximum borrowing amount EBP, Note Receivable from Participant, Account, Maximum Borrowing, Amount Common Collective Trust [Member] Common Trust Funds Amendment Flag EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash and Noncash EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash and Noncash, Total Contributions from employer, net of forfeitures EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] Deductions from net assets attributed to: EBP, Payment to Participant [Policy Text Block] Benefit Payments EBP, Schedule of Asset Held for Investment [Line Items] Fair Value Hierarchy and NAV [Axis] Employee Benefit Plan Schedule Of Assets Held At End Of Year [Text Block] Employee benefit plan schedule of assets held at end of year. Schedule of Assets (Held at End of Year) EBP, Investment, Current Value, Type [Extensible Enumeration] Investment Type [Axis] Document Type Entity Central Index Key Investment Valuation and Income Recognition EBP, Investment [Policy Text Block] EBP, Accounting Policy [Table] EBP, Basis of Accounting [Policy Text Block] Basis of Presentation Current Fiscal Year End Date EBP, Description of Plan [Table] EBP, Employer, Common Stock [Member] Company Common Stock EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment, Total Dividend and other income Employee Benefit Plan, Age Sixty through Sixty Three Participant Contribution, Catch Up Contribution Amount Amount of maximum catch-up contribution, employees aged 60 through 63 can make during the plan year. Participants age 60 through 63, catch-up contribution Investment counselor fees and other Employee Benefit Plan Change In Net Asset Available For Benefit Investment Counselor Fees and Other Employee benefit plan change in net asset available for benefit investment counselor fees and other. Minimum [Member] Minimum EBP 004 [Member] EBP 004. EBP 004 EBP, Related Party and Party-in-Interest Transactions [Text Block] Related Party Transactions EBP, Change in Net Asset Available for Benefit, Increase Total additions, net EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] Employee Benefit Plan Voting Rights [Abstract] Employee benefit plan voting rights. Document Information [Line Items] EBP, Nonparticipant-Directed Investment [Line Items] EBP, Statement of Net Asset Available for Benefit [Abstract] EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Excluding Rollover Contributions from participants EBP, Tax Determination Letter, Date Tax determination letter, date EBP, Participant Contribution, Automatic, Deferral Rate EBP, Automatic deferral rate EBP, Nonparticipant-Directed Investment [Abstract] EBP, Related Party and Party-in-Interest Transactions [Abstract] Employee benefit plans vested percentage Employee Benefit Plans Vested Percentage Employee benefit plans vested percentage. EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value, Ending Balance EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value, Beginning Balance EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value, Total Investments, at fair value EBP, Use of Estimate [Policy Text Block] Use of Estimates Mutual Fund [Member] Mutual Funds Entity [Domain] Employee Benefit Plan Voting Rights [Table] Employee benefit plan voting rights. EBP, Summary of Accounting Policy [Text Block] Summary of Significant Accounting Policies EBP, Investment, Fair Value and NAV [Text Block] Fair Value Measurements EBP, Description of Plan and Accounting Change [Abstract] EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution EBP, Statement of Change in Net Asset Available for Benefit [Line Items] Statistical Measurement [Domain] EBP, Note Receivable from Participant Notes receivable from participants Document Period End Date EBP, Risk and Uncertainty [Table] Fair Value Hierarchy and NAV [Domain] EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage Receivable from participants, account, maximum borrowing, to total account, percentage Tax determination letter, obtained EBP, Tax Determination Letter, Obtained [true false] Employee Benefit Plan, Involuntary Termination, Direct Payment to Participant Amount directly payable to participant upon termination of the plan without the participant’s consent. Involuntary termination, direct payment to participant EBP, Related Party and Party-in-Interest Transactions [Table] Employee Benefit Plan, Age Fifty or Older Participant Contribution, Catch Up Contribution Amount Amount of maximum catch-up contribution that can be made by participants of age 50 or older during the Plan year. Participants age 50 or older, catch-up contribution Involuntary terminations, automatic distribution of participant accounts Employee Benefit Plan Involuntary Termination, Automatic Distribution of Participant Accounts Amount of automatic distribution of participant accounts upon termination without the participant’s consent. Investments Measured at Fair Value Excluding Common Trust Funds [Member] Investments Measured at Fair Value Excluding Common Trust Funds [Member] Total Assets in the Fair Value Hierarchy Cover [Abstract] Investments [Domain] EBP, Risk and Uncertainty [Abstract] EBP, Net Asset Available for Benefit Net assets available for benefits, beginning of year Net assets available for benefits, end of year Net assets available for benefits Net assets available for benefits EBP, Investment, Fair Value and NAV [Table Text Block] Schedule of Investments Measured at Fair Value on a Recurring Basis EBP, Schedule of Asset Held for Investment [Abstract] EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value EBP, Note Receivable from Participant [Policy Text Block] Notes Receivable from Participants EBP, Schedule of Asset Held for Investment [Table Text Block] Schedule of Assets EBP, Statement of Net Asset Available for Benefit [Table] Document Fiscal Year Focus EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment, Total Net appreciation in fair value of investments EBP, Employer Contribution, Participant Compensation Matched, Percentage Percentage on employee's eligible compensation EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Asset Total assets EBP, Contribution [Policy Text Block] Contributions Non-Highly Compensated Employees [Member] Non-Highly Compensated Employees. Non-Highly Compensated Employees EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, Percentage Employee contribution percentage EBP, Plan Number EBP, Investment, Fair Value and NAV [Line Items] Document Information [Table] Legal Entity [Axis] EBP, Plan Name Employee Benefit Plan, Additional Employer Discretionary Contribution Amount of additional employer discretionary contribution. Additional employer discretionary contribution EBP, Risk and Uncertainty [Line Items] Employee Benefit Plan Participant Loan Fixed Rate Employee benefit plan notes receivable from participants fixed rate. Participant loan fixed rate EBP, Asset [Abstract] Assets: EBP, Investment, Fair Value and NAV [Table] EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Rollover Rollover contributions EBP, Accounting Policy, Accounting Standard Update, and Change in Accounting Principle [Abstract] EBP, Asset Held for Investment EBP, Asset Held for Investment, Total EBP, Tax Status [Text Block] Federal Income Tax Status Maximum [Member] Maximum EBP, Other Receivable Other receivables Statistical Measurement [Axis] EBP, Statement of Change in Net Asset Available for Benefit [Abstract] Employee Benefit Plan, Profit Sharing Contribution By Employer Amount of Profit sharing contribution made by the employer. Profit Sharing contribution Employee Benefit Plan Voting Rights [Line Items] Employee benefit plan voting rights. Entity Registrant Name EBP, Asset Held for Investment, Participant Loan, Interest Rate Participant loan interest rate EBP, Nonparticipant-Directed Investment [Table] Investments and Investment Options EBP, Nonparticipant-Directed Investment [Text Block] EBP, Related Party and Party-in-Interest [Domain] EBP, Related Party and Party-in-Interest [Axis] EBP, Risk and Uncertainty [Text Block] Risk and Uncertainties Total deductions EBP, Change in Net Asset Available for Benefit, Decrease Voting Rights Employee Benefit Plan Voting Rights [Text Block] The entire disclosure of employee benefit plan voting rights. Fair Value, Inputs, Level 1 [Member] Level 1 EBP, Tax Status [Line Items] Entity Tax Identification Number EBP, Asset Held for Investment, Participant Loan, Maturity Date Participant loan maturity date EBP, Change in Net Asset Available for Benefit, Increase (Decrease) Net increase EBP, Tax Status [Table] EBP, Asset Held for Investment, Party-in-Interest [true false] Dimensional Fund Advisors [Member] Kirby Corporation Common stock [Member] Kirby Corporation Common stock. Franklin Templeton [Member] Fidelity [Member] BlackRock. Invesco. T. Rowe Price [Member] Prudential Jennison. American Funds [Member] T. Rowe Price [Member] BlackRock [Member] Dimensional Fund Advisors. PIMCO [Member] American Century. Invesco [Member] Harbor. Northern Trust. American Century [Member] PIMCO. Franklin Templeton. American Funds. Prudential Jennison [Member] Northern Trust [Member] Harbor [Member] Fidelity.