Long-Term Debt and Related Matters (Narrative) (Details) £ in Thousands, $ in Thousands		12 Months Ended
	Mar. 13, 2015 USD ($)	Dec. 31, 2015 GBP (£)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 23, 2014 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate Description	Borrowings under the Amended Credit Agreement will bear interest at rates based upon either the base rate or Euro-rate plus applicable margins. Applicable margins are dictated by the ratio of L.B. Foster's indebtedness less consolidated cash on hand to L.B. Foster's consolidated EBITDA, as defined in the underlying Amended Credit Agreement. The base rate is the highest of (a) PNC Bank's prime rate, (b) the Federal Funds Rate plus 0.50% or (c) the daily Euro-rate (as defined in the Amended Credit Agreement) plus 1.00%. The base rate and Euro-rate spreads range from 0.00% to 1.50% and 1.00% to 2.50%, respectively.
Line of Credit Facility, Covenant Terms	The Amended Credit Agreement includes two financial covenants: (a) Leverage Ratio, defined as L.B. Foster's Indebtedness less consolidated cash on hand, in excess of $15,000, divided by L.B. Foster's consolidated EBITDA, which must not exceed 3.25 to 1.00 and (b) Minimum Interest Coverage, defined as consolidated EBITDA less Capital Expenditures divided by consolidated interest expense, which must be no less than 3.00 to 1.00.
Line of Credit Facility, Dividend Restrictions	The Amended Credit Agreement permits L.B. Foster to pay dividends, distributions, and make redemptions with respect to its stock provided no event of default or potential default (as defined in the Amended Credit Agreement) has occurred prior to or after giving effect to the dividend, distribution, or redemption. Dividends, distributions, and redemptions are capped at $25,000 per year when funds are drawn on the facility. If no drawings on the facility exist, dividends, distributions, and redemptions in excess of $25,000 per year are subjected to a limitation of $75,000 in the aggregate over the life of the facility. The $75,000 aggregate limitation also permits certain loans, investments, and acquisitions.
Line of Credit Facility, Amount Outstanding			$ 165,000	$ 24,200
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding			526	425
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A. and Citizens Bank of Pennsylvania [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Covenant Compliance		At December 31, 2015, the Company was in compliance with the Amended Credit Agreement's covenants
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A. and Citizens Bank of Pennsylvania [Member] | Prior Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					$ 200,000
Line of Credit Facility, Amount Outstanding				24,200
Line of Credit Facility, Current Borrowing Capacity				175,375
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A., Citizens Bank of Pennsylvania, and Branch Banking and Trust Company [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Initiation Date	Mar. 13, 2015
Line of Credit Facility, Maximum Borrowing Capacity	$ 335,000
Debt Instrument, Term	5 years
Line of Credit Facility, Provision for Increase in Capacity	$ 100,000
Line of Credit Facility, Amount Outstanding			165,000
Line of Credit Facility, Current Borrowing Capacity			169,474
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A., Citizens Bank of Pennsylvania, and Branch Banking and Trust Company [Member] | Revolving Credit Facility Available To Canadian Borrowers [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 25,000
NatWest Bank [Member] | Foreign Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		£ 1,500	2,210
Line of Credit Facility, Description		A subsidiary of the Company has a credit facility with NatWest Bank for its United Kingdom operations which includes an overdraft availability of £1,500 pounds sterling (approximately $2,210 at December 31, 2015). This credit facility supports the United Kingdom's working capital requirements and is collateralized by substantially all of the assets of its United Kingdom operations
Line of Credit Facility, Interest Rate Description		. The interest rate on this facility is the financial institution's base rate plus 1.50%.
Line of Credit Facility, Covenant Terms		The United Kingdom loan agreements contain certain financial covenants that require that subsidiary to maintain senior interest and cash flow coverage ratios. The subsidiary was in compliance with these financial covenants at December 31, 2015 and 2014.
Line of Credit Facility, Amount Outstanding			0
Line of Credit Facility, Current Borrowing Capacity			2,194	$ 2,337
Line of Credit Facility, Collateral		This credit facility supports the United Kingdom's working capital requirements and is collateralized by substantially all of the assets of its United Kingdom operations.
NatWest Bank Outstanding Guarantees [Member] | Foreign Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding			$ 16