| Cover | Aug. 03, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Aug. 3, 2021 |
| Entity Registrant Name | L.B. Foster Company |
| Entity Incorporation, State or Country Code | PA |
| Entity File Number | 000-10436 |
| Entity Tax Identification Number | 25-1324733 |
| Entity Address, Postal Zip Code | 15220 |
| Trading Symbol | FSTR |
| Security Exchange Name | NASDAQ |
| Title of 12(b) Security | Common Stock, Par Value $0.01 |
| Entity Address, Address Line One | 415 Holiday Drive, Suite 100, |
| Entity Address, City or Town | Pittsburgh, |
| Entity Address, State or Province | PA |
| City Area Code | 412 |
| Local Phone Number | 928-3400 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000352825 |
| Amendment Flag | false |
