Earning Per Common Share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator for basic and diluted earnings (loss) per common share:
Net income (loss) attributable to L.B. Foster Company	$ 4,436	$ (2,152)
Denominator:
Weighted average shares outstanding (in shares)	10,762,000	10,792,000
Denominator for basic earnings (loss) per common share (in shares)	10,762,000	10,792,000
Effect of dilutive securities:
Stock compensation plans (in shares)	223,000	0
Dilutive potential common shares (in shares)	223,000	0
Denominator for diluted earnings (loss) per common share - adjusted weighted average shares outstanding (in shares)	10,985,000	10,792,000
Basic earnings (loss) per common share (in USD per share)	$ 0.41	$ (0.20)
Diluted earnings (loss) per common share (in USD per share)	$ 0.40	$ (0.20)
Anti-dilutive shares (in shares)	0	101,000