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, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator for basic and diluted earnings per common share:
Net income (loss) attributable to L.B. Foster Company	$ 515	$ (2,077)	$ 1,894	$ (1,633)
Denominator:
Weighted average shares outstanding (in shares)	10,813	10,731	10,804	10,710
Denominator for basic earnings (loss) per common share (in shares)	10,813	10,731	10,804	10,710
Effect of dilutive securities:
Stock compensation plans (in shares)	160	0	91	0
Dilutive potential common shares (in shares)	160	0	91	0
Denominator for diluted earnings (loss) per common share - adjusted weighted average shares outstanding (in shares)	10,973	10,731	10,895	10,710
Basic earnings (loss) per common share (usd per share)	$ 0.05	$ (0.20)	$ 0.18	$ (0.16)
Diluted earnings (loss) per common share (usd per share)	$ 0.05	$ (0.20)	$ 0.17	$ (0.16)
Anti-dilutive shares (in shares)		109		108