Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Numerator for basic and diluted earnings per common share:
Net income attributable to L.B. Foster Company	$ 4,354	$ 35,905	$ 5,129	$ 43,188
Denominator:
Weighted average shares outstanding (in shares)	10,356	10,718	10,444	10,757
Denominator for basic earnings per common share (in shares)	10,356	10,718	10,444	10,757
Effect of dilutive securities:
Stock compensation plans (in shares)	524	274	479	302
Dilutive potential common shares (in shares)	524	274	479	302
Denominator for diluted earnings per common share - adjusted weighted average shares outstanding (in shares)	10,880	10,992	10,923	11,059
Basic earnings per common share (in USD per share)	$ 0.42	$ 3.35	$ 0.49	$ 4.01
Diluted earnings per common share (in USD per share)	$ 0.40	$ 3.27	$ 0.47	$ 3.91