Earning Per Common Share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator for basic and diluted earnings per common share:
Net income attributable to L.B. Foster Company	$ 35,905	$ 515	$ 43,188	$ 1,894
Denominator:
Weighted average shares outstanding (in shares)	10,718	10,813	10,757	10,804
Denominator for basic earnings per common share (in shares)	10,718	10,813	10,757	10,804
Effect of dilutive securities:
Stock compensation plans (in shares)	274	160	302	91
Dilutive potential common shares (in shares)	274	160	302	91
Denominator for diluted earnings per common share - adjusted weighted average shares outstanding (in shares)	10,992	10,973	11,059	10,895
Basic earnings per common share (in USD per share)	$ 3.35	$ 0.05	$ 4.01	$ 0.18
Diluted earnings per common share (in USD per share)	$ 3.27	$ 0.05	$ 3.91	$ 0.17

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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