Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Range [Domain] Statistical Measurement [Domain] Foreign Plan Foreign Plan [Member] Award Timing Predetermined Award Timing Predetermined [Flag] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Commission File Number Entity File Number Paid-in Capital Additional Paid-in Capital [Member] Tabular List, Table Tabular List [Table Text Block] Recently Issued Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Contract Liabilities Contract With Customer Liability [Roll Forward] Contract With Customer Liability Accounts payable Increase (Decrease) in Accounts Payable SOFR Secured Overnight Financing Rate (SOFR) [Member] Interest expense - net Interest expense - net Interest Income (Expense), Nonoperating Goodwill [Line Items] Goodwill [Line Items] Share-Based Payment Arrangement, Noncash Expense [Abstract] Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Basic earnings (loss) per common share (in USD per share) Basic earnings (loss) per common share (in USD per share) Earnings Per Share, Basic Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Number of potentially responsible parties included in agreement Number Of Potentially Responsible Parties Included In Agreement Number Of Potentially Responsible Parties Included In Agreement Revenue Revenue from Contract with Customer [Text Block] Infrastructure Solutions Infrastructure Solutions Infrastructure Solutions Segment [Member] Infrastructure Solutions Segment Schedule of Segment Reporting Information, by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Inventory Disclosure [Abstract] Debt Instrument, Redemption, Period [Axis] Debt Instrument, Redemption, Period [Axis] Revenue remaining performance obligation Revenue, Remaining Performance Obligation, Amount Adjustment to Compensation, Amount Adjustment to Compensation Amount Revenue remaining performance obligation Revenue, Remaining Performance Obligation, Percentage Stock-based compensation Share-Based Payment Arrangement, Noncash Expense Employee Stock Option Share-Based Payment Arrangement, Option [Member] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Unrealized loss on cash flow hedge, tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, Tax Total L.B. Foster Company stockholders’ equity Equity, Attributable to Parent Other comprehensive (loss) income, net of tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Insider Trading Policies and Procedures [Line Items] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Goodwill and Intangible Assets Disclosure [Abstract] Patents Patents [Member] Common shares issues net of shares withheld (in shares) Stock Issued During Period, Shares, New Issues Current assets: Assets, Current [Abstract] TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY Liabilities and Equity LIABILITIES AND STOCKHOLDERS’ EQUITY Liabilities and Equity [Abstract] Cover [Abstract] Maximum Maximum [Member] Weighted Average Amortization Period In Years Finite-Lived Intangible Asset, Useful Life Net loss attributable to noncontrolling interest Net loss attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Expenditures for Long-Lived Assets Segment, Expenditure, Addition to Long-Lived Assets Accounting Policies [Abstract] Other intangibles - net (Note 4) Net Carrying Amount Finite-Lived Intangible Assets, Net Restricted Stock Restricted Stock [Member] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Treasury Stock Treasury Stock, Common [Member] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Retirement Benefits [Abstract] Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Debt Instrument, Redemption, Period One Debt Instrument, Redemption, Period One [Member] Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Income (loss) before income taxes Income (loss) before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Other long-term liabilities Other Liabilities, Noncurrent Debt Instrument, Redemption, Period [Domain] Debt Instrument, Redemption, Period [Domain] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Operating Segments Operating Segments [Member] Unrealized gain (loss) on cash flow hedges, net of tax expense of $0 Unrealized derivative gain (loss) on cash flow hedges Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount Amounts attributable to noncontrolling interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Line of Credit Facility [Table] Line of Credit Facility [Table] Other long-term liabilities Increase (Decrease) in Other Noncurrent Liabilities Comprehensive income (loss) attributable to L.B. Foster Company Comprehensive Income (Loss), Net of Tax, Attributable to Parent Name Measure Name Balance as of December 31, 2025 Balance as of March 31, 2026 Restructuring Reserve Net income (loss) attributable to L.B. Foster Company Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Letter of Credit Letter of Credit [Member] Deferred tax liabilities (Note 9) Deferred Income Tax Liabilities, Net Document Fiscal Period Focus Document Fiscal Period Focus Award Timing Method Award Timing Method [Text Block] Favorable lease Off-Market Favorable Lease [Member] Award Type [Axis] Award Type [Axis] TOTAL ASSETS Assets Assets Trading Symbol Trading Symbol Weighted average shares vested (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Anticipated clean period Remedial Work Anticipated Clean Up Period Remedial Work Anticipated Clean Up Period Entity Address, City Entity Address, City or Town CASH FLOWS FROM OPERATING ACTIVITIES: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Inventory Inventory Disclosure [Text Block] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Restricted Stock Units Restricted Stock Units (RSUs) [Member] Statement of Income Location, Balance [Domain] Statement of Income Location, Balance [Domain] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Entity Emerging Growth Company Entity Emerging Growth Company Entity Common Stock, Shares Outstanding (in shares) Entity Common Stock, Shares Outstanding Number of stock options outstanding (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Total net sales Net sales Revenue from Contract with Customer, Including Assessed Tax Restructuring Liability Restructuring Reserve [Roll Forward] Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Over time input method Over Time Input Method [Member] Over Time Input Method Net expense Current period provision Accounts Receivable, Credit Loss Expense (Reversal) Plan Name [Axis] Plan Name [Axis] PEO PEO [Member] Accounts Receivable Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Revenue recognized but not yet billed Contract With Customer, Asset, Revenue Recognized But Not Yet Billed Contract With Customer, Asset, Revenue Recognized But Not Yet Billed Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Steel Products Steel Products Segment [Member] Steel Products Segment Fifth Amended And Restated Credit Agreement Fifth Amended And Restated Credit Agreement [Member] Fifth Amended And Restated Credit Agreement United States UNITED STATES Change in operating assets and liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Retained Earnings Retained Earnings [Member] Number of financial covenants Debt Instrument, Number Of Financial Covenants Debt Instrument, Number Of Financial Covenants Restricted Stock and Performance Share Units Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income tax benefit Income tax expense (benefit) Income Tax Expense (Benefit) Debt instrument, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Products and Services [Domain] Product and Service [Domain] Net income (loss) Net loss Net income (loss) Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Number of parties required to perform remedial design work Number Of Parties Required To Perform Remedial Work Number Of Parties Required To Perform Remedial Work Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Other current assets Increase (Decrease) in Other Current Assets Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] City Area Code City Area Code Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Number of defined contribution plans Number Of Defined Contribution Plans Number Of Defined Contribution Plans Other accrued liabilities Accrued Liabilities, Current Outstanding, beginning balance (in shares) Outstanding, ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Minimum leverage ratio Debt Instrument, Covenant, Leverage Ratio, Maximum Debt Instrument, Covenant, Leverage Ratio, Maximum Commitments and Contingencies Disclosure [Abstract] Schedule of Contract with Customer, Contract Asset, Contract Liability Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] General administrative costs General and Administrative Expense CASH FLOWS FROM INVESTING ACTIVITIES: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Net cash used in operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Minimum fixed charge coverage ratio Debt Instrument, Covenant, Interest Coverage Ratio, Minimum Debt Instrument, Covenant, Interest Coverage Ratio, Minimum Debt instrument term Debt Instrument, Term Selling, General and Administrative Expenses Selling, General and Administrative Expenses [Member] Goodwill (Note 4) Balance as of December 31, 2025 Balance as of March 31, 2026 Goodwill Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Depreciation Depreciation Denominator: Weighted Average Number of Shares Outstanding, Basic [Abstract] Over time sales, amount Over Time Sales, Amount Over Time Sales, Amount Equity Components [Axis] Equity Components [Axis] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Sales of goods Product [Member] Number of reportable segments Number of Reportable Segments Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Other Performance Measure, Amount Other Performance Measure, Amount Entity Address, State Entity Address, State or Province Total current liabilities Liabilities, Current Purchased services Purchased Services Expense Purchased Services Expense Individual: Individual [Axis] Expenses associated with contributions made Defined Contribution Plan, Cost Other current assets Other Assets, Current Net cash used in investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Amortization Amortization expense Amortization Revenue, remaining performance obligation, expected timing of satisfaction, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity Undiscovered remedial work Undiscovered Remedial Work Undiscovered Remedial Work Document Fiscal Year Focus Document Fiscal Year Focus Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Lender Name [Axis] Lender Name [Axis] Operating lease right-of-use assets - net Operating Lease, Right-of-Use Asset Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Contract Assets Contract With Customer Asset After Allowance For Credit Loss Current [Roll Forward] Contract With Customer Asset After Allowance For Credit Loss Current Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Entity Interactive Data Current Entity Interactive Data Current Plan Name [Domain] Plan Name [Domain] Recognition period for compensation expense not yet recognized Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Business Segments Segment Reporting Disclosure [Text Block] Goodwill [Table] Goodwill [Table] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Current maturities of long-term debt (Note 7) Less current maturities Long-Term Debt and Lease Obligation, Current Total Debt and Lease Obligation Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Axis] Finite-Lived Intangible Assets Finite-Lived Intangible Assets [Line Items] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Weighted Average Amortization Period In Years Weighted Average [Member] Amortization expense Amortization of Intangible Assets Selling and administrative expenses Selling, General and Administrative Expense Deferred tax assets (Note 9) Deferred Income Tax Assets, Net Purchase of common shares for treasury Stock Repurchased During Period, Value Accounts Receivable Additional Disclosures [Abstract] Depreciation/Amortization Depreciation, Depletion and Amortization Other assets Other Assets, Noncurrent Entity Central Index Key Entity Central Index Key PEO Name PEO Name Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] PNC Bank, N.A., Bank of America, N.A., Citizens Bank, N.A., and Wells Fargo Bank N.A. as Co-Syndication Agents, and Dollar Bank, Federal Savings Bank as a Participant PNC Bank, N.A., Bank Of America, N.A., Citizens Bank, N.A., And Wells Fargo Bank N.A. As Co-Syndication Agents, And Dollar Bank, Federal Savings Bank As Participant [Member] PNC Bank N.A. Citizens Bank N.A. Wells Fargo Bank National Association Bank of America N.A. And BMO Harris Bank National Association Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Revolving credit facility Revolving Credit Facility [Member] Defined Benefit Plan [Table] Defined Benefit Plan [Table] Finance leases and financing agreements Finance Lease, Liability Arrangement Duration Trading Arrangement Duration Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Technology Services and Solutions Rail Technologies Products [Member] Rail Technologies Products Deferred revenue (Note 3) Contract with Customer, Liability, Current Segments [Axis] Segments [Axis] Work-in-process Inventory, Work in Process, Net of Reserves Less comprehensive income attributable to noncontrolling interest: Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest [Abstract] Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Local Phone Number Local Phone Number Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Stock-Based Compensation Share-Based Payment Arrangement [Text Block] Incremental Loans Incremental Loans [Member] Incremental Loans ASSETS Assets [Abstract] Credit Facility [Axis] Credit Facility [Axis] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Debt Instrument [Axis] Debt Instrument [Axis] Weighted average grant date fair value, cancelled and forfeited (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Retirement Plans Retirement Benefits [Text Block] Credit Facility [Domain] Credit Facility [Domain] Gross Carrying Value Finite-Lived Intangible Assets, Gross Stockholders’ equity: Equity, Attributable to Parent [Abstract] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Entity Address, Street Name Entity Address, Address Line One Entity Address, Suite Entity Address, Address Line Two Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Long-term operating lease liabilities Operating Lease, Liability, Noncurrent Fair Value as of Grant Date Award Grant Date Fair Value Entity Registrant Name Entity Registrant Name Other noncurrent assets Increase (Decrease) in Other Noncurrent Assets Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Selling and administrative employment costs Labor and Related Expense Schedule of Long-term Debt Instruments Schedule of Long-Term Debt Instruments [Table Text Block] Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Title and Position [Domain] Title and Position [Domain] Cancelled and forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Expected cost on shares expected to vest Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Debt Instrument, Redemption, Period Two Debt Instrument, Redemption, Period Two [Member] Document Quarterly Report Document Quarterly Report Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Number of operating segments Number of Operating Segments Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Weighted average shares granted (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Sales of services Service [Member] Schedule of Finite-Lived Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Schedule of Sales by Major Product Line Schedule of Revenues by Major Product Line [Table Text Block] Tabular disclosure summarizing sales by major product line. Restatement Determination Date: Restatement Determination Date [Axis] Non-PEO NEO Non-PEO NEO [Member] Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest Corporate management stock-based compensation Corporate Management Stock-based Compensation Corporate Management Stock-based Compensation Stock compensation plans (in shares) Incremental Common Shares Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends Swing Loan Swing Loan [Member] Swing Loan Name Trading Arrangement, Individual Name Award Type [Domain] Award Type [Domain] Noncontrolling interest Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Disaggregation of Revenue Disaggregation of Revenue [Line Items] Defined Benefit Plan Disclosure Defined Benefit Plan Disclosure [Line Items] Canada CANADA Accounts receivable Increase (Decrease) in Accounts and Other Receivables Compensation Amount Outstanding Recovery Compensation Amount Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Statement of Comprehensive Income [Abstract] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Revenue recognized from contract liabilities Contract with Customer, Liability, Revenue Recognized Accrued payroll and employee benefits Increase (Decrease) in Employee Related Liabilities Schedule of Accounts Receivable, Allowance for Credit Loss Accounts Receivable, Allowance for Credit Loss [Table Text Block] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Name Awards Close in Time to MNPI Disclosures, Individual Name Number of companies that received a general notice letter (company) Number Of Companies Receiving General Notice Letter Number Of Companies Receiving General Notice Letter Weighted average share price, beginning balance (in USD per share) Weighted average share price, ending balance (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Cash paid Payments for Restructuring Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Stock-based compensation APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Present value of remedial work Present Value Of Proposed Remedial Work Present Value Of Proposed Remedial Work Omnibus Plan and Equity and Incentive Plan Omnibus Plan And Equity And Incentive Plan [Member] Omnibus Plan And Equity And Incentive Plan Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Long-term debt (Note 7) Long-term portion Long-Term Debt and Lease Obligation Defined Contribution Plan Disclosure Defined Contribution Plan Disclosure [Line Items] Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] Segments [Domain] Segments [Domain] Statement of Income Location, Balance [Axis] Statement of Income Location, Balance [Axis] Performance-Based Stock and Stock Units Performance Shares [Member] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Rail, Technologies, and Services Rail Technologies And Services Segment [Member] Rail Technologies And Services Segment Inventories Increase (Decrease) in Inventories Inventories - net (Note 6) Inventories - net Inventory, Net Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Minimum Minimum [Member] Company Selected Measure Name Company Selected Measure Name Accrual for environmental loss Accrual for Environmental Loss Contingencies Long-Term Debt and Related Matters Debt Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Accounts payable Accounts Payable, Current Defined Contribution Plan [Table] Defined Contribution Plan [Table] Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] All Executive Categories All Executive Categories [Member] Finished goods Inventory, Finished Goods, Net of Reserves Common stock, par value $0.01, authorized 20,000,000 shares; shares issued at March 31, 2026 and December 31, 2025, 11,115,779; shares outstanding at March 31, 2026 and December 31, 2025, 10,326,247 and 10,135,410, respectively Common Stock, Value, Issued Goodwill Goodwill [Roll Forward] Restructuring Plan [Domain] Restructuring Plan [Domain] Commitments and Contingent Liabilities Commitments and Contingencies Disclosure [Text Block] Title and Position [Axis] Title and Position [Axis] Other assets: Other Assets, Noncurrent [Abstract] Daily Simple SOFR Daily Simple SOFR [Member] Daily Simple SOFR AMH Automation And Materials Handling [Member] Automation And Materials Handling Diluted weighted average shares outstanding (in shares) Denominator for diluted earnings (loss) per common share - adjusted weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Total comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Entity Small Business Entity Small Business Income Tax Disclosure [Abstract] Schedule of Nonvested Share Activity Schedule of Nonvested Share Activity [Table Text Block] Noncontrolling Interest Noncontrolling Interest [Member] Document Transition Report Document Transition Report Underlying Securities Award Underlying Securities Amount Automation and Materials Handling Line Automation and Materials Handling Line [Member] Automation and Materials Handling Line Repayments of debt Repayments of Other Long-Term Debt Equity Component [Domain] Equity Component [Domain] Document Period End Date Document Period End Date PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Income Taxes Income Tax Disclosure [Text Block] Allowance for doubtful accounts, beginning balance Allowance for doubtful accounts, ending balance Accounts Receivable, Allowance for Credit Loss Precast Concrete Products Precast Concrete Products Segment [Member] Precast Concrete Products Segment United Kingdom UNITED KINGDOM Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Revenue from Contract with Customer [Abstract] Total stockholders’ equity Beginning balance Ending balance Equity, Including Portion Attributable to Noncontrolling Interest Document Type Document Type Earnings Per Common Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Paid-in capital Additional Paid in Capital Products and Services [Axis] Product and Service [Axis] Domestic Plan Domestic Plan [Member] Financing Receivable, Allowance for Credit Loss [Table] Financing Receivable, Allowance for Credit Loss [Table] All Individuals All Individuals [Member] Capital expenditures on property, plant, and equipment Payments to Acquire Property, Plant, and Equipment Point in time Transferred at Point in Time [Member] Name Forgone Recovery, Individual Name Total current assets Assets, Current Range [Axis] Statistical Measurement [Axis] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Public company costs Public Company Costs Public Company Costs Weighted average shares outstanding (in shares) Weighted Average Number of Shares Issued, Basic Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Foreign currency translation impact Goodwill, Foreign Currency Translation, Gain (Loss) Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Intangible Asset, Finite-Lived [Table] Intangible Asset, Finite-Lived [Table] Current liabilities: Liabilities, Current [Abstract] Line of Credit Facility Line of Credit Facility [Line Items] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Revolving credit facility Long-Term Line of Credit Diluted earnings (loss) per common share (in USD per share) Diluted earnings (loss) per common share (in USD per share) Earnings Per Share, Diluted Other current liabilities Increase (Decrease) in Other Accrued Liabilities Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Title of 12(b) Security Title of 12(b) Security Corporate And Reconciling Items Corporate And Reconciling Items [Member] Corporate And Reconciling Items Over time sales, percentage Over Time Sales, Percent Over Time Sales, Percent Other comprehensive income, net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Treasury stock shares - at cost, common stock (in shares) Treasury Stock, Common, Shares Per share data attributable to L.B. Foster shareholders: Earnings Per Share [Abstract] Restructuring Plan [Axis] Restructuring Plan [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Gross profit Gross Profit Deferred revenue Increase (Decrease) in Contract with Customer, Liability Effect of dilutive securities: Weighted Average Number of Shares Outstanding, Diluted, Adjustment [Abstract] Financing Receivable, Allowance for Credit Loss [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] Income taxes paid Income Taxes Paid, Net Award Timing Disclosures [Line Items] Number of board members Number Of Board Members Elected To Receive Fully Vested Stock Number Of Board Members Elected To Receive Fully Vested Stock Schedule of Inventory Schedule of Inventory, Current [Table Text Block] Accrued payroll and employee benefits Employee-related Liabilities, Current Recoveries of previous write-offs Accounts Receivable, Allowance for Credit Loss, Recovery Proceeds from debt Proceeds from Issuance of Other Long-Term Debt Property, plant, and equipment - net Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization Net income (loss) attributable to L.B. Foster Company Net Income (Loss) Attributable to Parent Expiration Date Trading Arrangement Expiration Date Vesting period Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Allowance for Credit Losses Accounts Receivable, Allowance for Credit Loss [Roll Forward] Timing of Transfer of Good or Service [Axis] Timing of Transfer of Good or Service [Axis] Segment Reporting Information Segment Reporting Information [Line Items] Numerator for basic and diluted earnings (loss) per common share: Net Income (Loss) Attributable to Parent [Abstract] Treasury stock acquisitions Payments for Repurchase of Common Stock Adoption Date Trading Arrangement Adoption Date Base Rate Base Rate [Member] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Contract assets - net (Note 3) Balance as of December 31, 2025 Balance as of March 31, 2026 Contract with Customer, Asset, after Allowance for Credit Loss Entity Current Reporting Status Entity Current Reporting Status Global Friction Management Global Friction Management [Member] Global Friction Management Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Customer relationships Customer Relationships [Member] Operating income (loss) Operating Income (Loss) Retained earnings Retained Earnings (Accumulated Deficit) Statement of Financial Position [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Executive Category: Executive Category [Axis] Over time Transferred over Time [Member] Current Fiscal Year End Date Current Fiscal Year End Date Technology Technology-Based Intangible Assets [Member] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Weighted Average Grant Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Other income - net Other income - net Other Nonoperating Income (Expense) Statement [Table] Statement [Table] Increase in billings in excess of cost, excluding revenue recognized Contract With Customer, Liability, Increase From Cash Receipts Contract With Customer, Liability, Increase From Cash Receipts Effect of exchange rate changes on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation Deferred income taxes Deferred Income Tax Expense (Benefit) Adjustments to reconcile net income (loss) to cash used in operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] CASH FLOWS FROM FINANCING ACTIVITIES: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Variable Rate [Domain] Variable Rate [Domain] Balance as of December 31, 2025 Balance as of March 31, 2026 Contract with Customer, Liability Timing of Transfer of Good or Service [Domain] Timing of Transfer of Good or Service [Domain] Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Antidilutive shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount All Adjustments to Compensation All Adjustments to Compensation [Member] Amendment Flag Amendment Flag Over time output method Over Time Output Method [Member] Over Time Output Method Treasury stock - at cost, 789,532 and 980,369 common stock shares at March 31, 2026 and December 31, 2025, respectively Treasury Stock, Common, Value Termination Date Trading Arrangement Termination Date Net cash provided by financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Contract assets Increase (Decrease) in Contract with Customer, Asset Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] Raw materials Inventory, Raw Materials, Net of Reserves Equity in income of nonconsolidated investments Equity (Loss) Income And Remeasurement Gain Equity (Loss) Income And Remeasurement Gain Basic weighted average shares outstanding (in shares) Denominator for basic earnings (loss) per common share (in shares) Weighted Average Number of Shares Outstanding, Basic Schedule of Earnings (Loss) Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Director Director [Member] Transfers from contract asset balance to accounts receivable Contract with Customer, Asset, Reclassified to Receivable Segment Reporting [Abstract] Total cost of sales Cost of sales Cost of Revenue Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Debt Disclosure [Abstract] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Entity Tax Identification Number Entity Tax Identification Number Corporate executive management costs Corporate Executive Management Costs Corporate Executive Management Costs Write-off against allowance Accounts Receivable, Allowance for Credit Loss, Writeoff Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Share-based Compensation Arrangement by Share-based Payment Award Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Common stock, par value (in USD per share) Common Stock, Par or Stated Value Per Share Common stock, shares issued (in shares) Common Stock, Shares, Issued Goodwill and Other Intangible Assets Goodwill and Intangible Assets Disclosure [Text Block] Rail Products Rail Products [Member] Rail Products Schedule of Goodwill Schedule of Goodwill [Table Text Block] Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Accounts receivable - net (Note 5) Accounts and Financing Receivable, after Allowance for Credit Loss, Current Insider Trading Arrangements [Line Items] Corporate Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Security Exchange Name Security Exchange Name Line of credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Schedule of Costs of Retirement Plans Schedule of Costs of Retirement Plans [Table Text Block] Purchase of common shares for treasury (in shares) Stock Repurchased During Period, Shares Overnight Bank Funding Rate Overnight Bank Funding Rate [Member] Overnight Bank Funding Rate Less: Operating Expenses [Abstract] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Trademarks and trade names Trademarks and Trade Names [Member] Issuance of common shares, net of share withheld for taxes Stock Issued During Period, Value, New Issues Statement Statement [Line Items] Variable Rate [Axis] Variable Rate [Axis] Consolidation Items [Axis] Consolidation Items [Axis] Schedule of Restructuring Reserve Schedule of Restructuring Reserve by Type of Cost [Table Text Block] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Cash and cash equivalents Cash and Cash Equivalent Common Stock Common Stock [Member] Vested (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Restricted Stock and Performance Shares Restricted Stock And Performance Shares Combined [Member] Restricted Stock And Performance Shares Combined Net (decrease) increase in cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Dilutive potential common shares (in shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment