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(Expense) Name Awards Close in Time to MNPI Disclosures, Individual Name 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] Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest Cancelled and forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period 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 General administrative costs General and Administrative Expense Adjustment to Compensation: Adjustment to Compensation [Axis] Schedule of Costs of Retirement Plans Schedule of Costs of Retirement Plans [Table Text Block] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity Statement of Cash Flows [Abstract] Over time output method Over Time Output Method [Member] Over Time Output Method Credit Facility [Axis] Credit Facility [Axis] Restructuring Costs Restructuring and Related Activities Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Long-term debt (Note 7) Long-term portion Long-Term Debt and Lease Obligation Name Measure Name Income Taxes Income Tax Disclosure [Text Block] Accounts payable Accounts Payable, Current Pay vs Performance Disclosure [Line Items] Equity in income of nonconsolidated investments Equity (Loss) Income And Remeasurement Gain Equity (Loss) Income And Remeasurement Gain Other current assets Increase (Decrease) in Other Current Assets Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Paid-in Capital Additional Paid-in Capital [Member] Entity Filer Category Entity Filer Category Defined Contribution Plan [Table] Defined Contribution Plan [Table] Director Director [Member] Personnel expenses Personnel Expenses Personnel Expenses Corporate executive management costs Corporate Executive Management Costs Corporate Executive Management Costs Name Trading Arrangement, Individual Name Cash and cash equivalents Cash and Cash Equivalent Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Axis] Raw materials Inventory, Raw Materials, Net of Reserves Company Selected Measure Amount Company Selected Measure Amount Less comprehensive income attributable to noncontrolling interest: Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest [Abstract] Depreciation/Amortization Depreciation, Depletion and Amortization Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] SOFR Secured Overnight Financing Rate (SOFR) [Member] Entity Address, Suite Entity Address, Address Line Two Net income Net income Net income Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Current assets: Assets, Current [Abstract] Rail Products Rail Products [Member] Rail Products Non-PEO NEO Non-PEO NEO [Member] Entity Address, Street Name Entity Address, Address Line One 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 Income tax expense Income tax expense Income Tax Expense (Benefit) Technology Technology-Based Intangible Assets [Member] Award Timing Method Award Timing Method [Text Block] Net 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 Accounts receivable - net (Note 5) Accounts and Financing Receivable, after Allowance for Credit Loss, Current Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Numerator for basic and diluted earnings per common share: Net Income (Loss) Attributable to Parent [Abstract] Net income attributable to L.B. Foster Company Net Income (Loss) Attributable to Parent Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Proceeds from the sale of property, plant, and equipment Proceeds from Sale of Property, Plant, and Equipment Statement [Table] Statement [Table] Overnight Bank Funding Rate Overnight Bank Funding Rate [Member] Overnight Bank Funding Rate Restatement Determination Date: Restatement Determination Date [Axis] Schedule of Contract with Customer, Contract Asset, Contract Liability Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Net income attributable to L.B. Foster Company Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Restricted Stock and Performance Shares Restricted Stock And Performance Shares Combined [Member] Restricted Stock And Performance Shares Combined Recoveries of previous write-offs Accounts Receivable, Allowance for Credit Loss, Recovery Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block]