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Revenue (Timing of Transfer) (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Disaggregation of Revenue |  |
Total net sales | $ 122,454 | $ 118,702
Point in time |  |
Disaggregation of Revenue |  |
Total net sales | 91,232 | 91,129
Over time |  |
Disaggregation of Revenue |  |
Total net sales | 31,222 | 27,573
Rail Products and Services |  |
Disaggregation of Revenue |  |
Total net sales | 62,170 | 56,480
Rail Products and Services | Point in time |  |
Disaggregation of Revenue |  |
Total net sales | 45,871 | 45,566
Rail Products and Services | Over time |  |
Disaggregation of Revenue |  |
Total net sales | 16,299 | 10,914
Construction Products |  |
Disaggregation of Revenue |  |
Total net sales | 28,900 | 37,322
Construction Products | Point in time |  |
Disaggregation of Revenue |  |
Total net sales | 18,926 | 24,624
Construction Products | Over time |  |
Disaggregation of Revenue |  |
Total net sales | 9,974 | 12,698
Tubular and Energy Services |  |
Disaggregation of Revenue |  |
Total net sales | 31,384 | 24,900
Tubular and Energy Services | Point in time |  |
Disaggregation of Revenue |  |
Total net sales | 26,435 | 20,939
Tubular and Energy Services | Over time |  |
Disaggregation of Revenue |  |
Total net sales | $ 4,949 | $ 3,961

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