Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net loss		$ (1,270)	$ (1,866)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment		453	(3,707)
Unrealized loss on cash flow hedges, net of tax benefit of $0 and $296, respectively		0	(864)
Cash flow hedges reclassified to earnings, net of tax expense of $98 and $0, respectively		136	0
Reclassification of pension liability adjustments to earnings, net of tax expense of $24 and $24, respectively*	[1]	91	58
Comprehensive loss attributable to L.B. Foster Company		(590)	(6,379)
Less comprehensive loss attributable to noncontrolling interest:
Net loss attributable to noncontrolling interest		(12)	0
Foreign currency translation adjustment		(30)	0
Amounts attributable to noncontrolling interest		(42)	0
Comprehensive loss attributable to L.B. Foster Company		$ (548)	$ (6,379)

[1] Reclassifications out of “Accumulated other comprehensive loss” for pension obligations are charged to “Selling and administrative expenses” within the Condensed Consolidated Statements of Operations.