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
	Mar. 31, 2021	Mar. 31, 2020
Numerator for basic and diluted loss per common share:
Loss from continuing operations attributable to L.B. Foster Company	$ (1,270)	$ (5)
Loss from discontinued operations	0	(1,861)
Net loss	(1,270)	(1,866)
Net loss attributable to L.B. Foster Company	$ (1,258)	$ (1,866)
Denominator:
Weighted average shares outstanding (in shares)	10,583	10,478
Denominator for basic loss per common share (in shares)	10,583	10,478
Effect of dilutive securities:
Stock compensation plans (in shares)	0	0
Dilutive potential common shares (in shares)	0	0
Denominator for diluted earnings (loss) per common share - adjusted weighted average shares outstanding (in shares)	10,583	10,478
Continuing operations (usd per share)	$ (0.12)	$ (0.00)
Discontinued operations (usd per share)	0	(0.18)
Basic earnings per common share (usd per share)	(0.12)	(0.18)
Continuing operations (usd per share)	(0.12)	(0.00)
Discontinued operations (usd per share)	0	(0.18)
Diluted earnings per common share (usd per share)	$ (0.12)	$ (0.18)
Anti-dilutive shares (in shares)	140	190