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Fair Value Measurements (Narratives) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |  |
Interest expense | $ 8,377 | $ 6,551 | $ 4,378
Lb Pipe Coupling Products Llc |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |  |
Impairment of long lived assets to be disposed of | 413 |  |
Swap |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis |  |  |
Notional amount | 50,000 |  |
Interest expense | $ 378 |  |

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- Definition The aggregate amount of write-downs for impairments recognized during the period for long-lived assets held for abandonment, exchange or sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2611-110228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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