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Business Segment - Sales by Major Product Line (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018
Revenue from External Customer |  |  |  |  |  |  |  |  |  |
Net Sales | $ 149,379 | $ 154,276 | $ 200,933 | $ 150,469 | $ 164,531 | $ 167,094 | $ 172,890 | $ 122,454 | $ 655,057 | $ 626,969
Rail Products |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |
Net Sales |  |  |  |  |  |  |  |  | 194,464 | 188,590
Rail Technologies |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |
Net Sales |  |  |  |  |  |  |  |  | 127,344 | 130,934
Piling and Fabricated Bridges Products |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |
Net Sales |  |  |  |  |  |  |  |  | 114,076 | 102,246
Protective Coating and Measurement Systems |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |
Net Sales |  |  |  |  |  |  |  |  | 99,760 | 89,026
Test , Inspection and Threading Services |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |
Net Sales |  |  |  |  |  |  |  |  | 68,410 | 56,407
Precast Concrete Products |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |
Net Sales |  |  |  |  |  |  |  |  | $ 51,003 | $ 59,766

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