Financial Statements (Policies)	9 Months Ended
Financial Statements (Policies)	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 8 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all estimates and adjustments (consisting of normal recurring accruals, unless otherwise stated herein) considered necessary for a fair presentation of the financial position of L.B. Foster Company and subsidiaries as of September 30, 2021 and December 31, 2020 and its Condensed Consolidated Statements of Operations, Condensed Consolidated Statements of Comprehensive Income, and Condensed Consolidated Statements of Stockholders’ Equity for the three and nine months ended September 30, 2021 and 2020 and its Condensed Consolidated Statements of Cash Flows for the nine months ended September 30, 2021 and 2020 have been included. However, actual results could differ from those estimates and changes in those estimates are recorded when known. The results of operations for interim periods are not necessarily indicative of the results that may be expected for the year ending December 31, 2021. The Condensed Consolidated Balance Sheet as of December 31, 2020 was derived from audited financial statements. This Quarterly Report on Form 10-Q should be read in conjunction with the consolidated financial statements and footnotes thereto included in L.B. Foster Company’s Annual Report on Form 10-K for the year ended December 31, 2020. In this Quarterly Report on Form 10-Q, references to “we,” “us,” “our,” and the “Company” refer collectively to L.B. Foster Company and its consolidated subsidiaries.
Reclassifications	Reclassifications Certain accounts in the prior year consolidated financial statements have been reclassified for comparative purposes principally to conform to the presentation of the current year period. Effective for the quarter ended September 30, 2020, the Company classified IOS Acquisitions, LLC and subsidiaries (“Test and Inspection Services”) as a discontinued operation. Effective for the quarter and year ended December 31, 2020, the Company implemented operational changes in how its Chief Operating Decision Maker (“CODM”) manages its businesses, including resource allocation and operating decisions. As a result of these changes, the Company now has two operating segments, Rail Technologies and Services and Infrastructure Solutions, representing the individual businesses that are run separately under the new structure. The Company has revised the information for all periods presented in this Quarterly Report on Form 10-Q to reflect these reclassifications.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In March 2020 and as clarified in January 2021, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. (“ASU”) 2020-04, “Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting” (“ASU 2020-04”), which provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships, and other transactions affected by the discontinuation of the London Interbank Offered Rate (“LIBOR”) or by another reference rate expected to be discontinued. The amendments are effective for all entities as of March 12, 2020 through December 31, 2022. The Company is currently evaluating the impacts of the provisions of ASU 2020-04 on its financial condition, results of operations, and cash flows.
Inventory	Inventories of the Company are valued at average cost or net realizable value, whichever is lower. Contract assets consist of costs and earnings in excess of billings, retainage, and other unbilled amounts generated when revenue recognized exceeds the amount billed to the customer.
Share Based Compensation	The Company applies the provisions of the FASB’s Accounting Standards Codification (“ASC”) Topic 718, “Compensation – Stock Compensation,” to account for the Company’s stock-based compensation. Stock-based compensation cost is measured at the grant date based on the calculated fair value of the award and is recognized over the employees’ requisite service periods.

Disclosure of inventory accounting policy for inventory classes, including, but not limited to, basis for determining inventory amounts, methods by which amounts are added and removed from inventory classes, loss recognition on impairment of inventories, and situations in which inventories are stated above cost.