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Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Disaggregation of Revenue [Line Items] |  |
Net sales: | $ 215,337 | $ 206,605
Renewable Energy & Conservation |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 56,986 | 51,792
Industrial and Infrastructure Products |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 54,624 | 50,718
Residential Products |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 103,948 | 104,551
Intersegment Elimination |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | (221) | (456)
Intersegment Elimination | Industrial and Infrastructure Products |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 54,403 | 50,262
Point in Time |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 155,047 | 160,606
Point in Time | Renewable Energy & Conservation |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 5,620 | 5,793
Point in Time | Residential Products |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 102,884 | 104,551
Point in Time | Intersegment Elimination | Industrial and Infrastructure Products |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 46,543 | 50,262
Over Time |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 60,290 | 45,999
Over Time | Renewable Energy & Conservation |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 51,366 | 45,999
Over Time | Residential Products |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | 1,064 | 0
Over Time | Intersegment Elimination | Industrial and Infrastructure Products |  |
Disaggregation of Revenue [Line Items] |  |
Net sales: | $ 7,860 | $ 0

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- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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