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Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Net sales:	$ 266,036	$ 247,627	$ 481,373	$ 454,232
Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	131,128	127,252	235,076	231,803
Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	61,193	57,612	115,596	107,874
Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	73,715	62,763	130,701	114,555
Point in Time
Disaggregation of Revenue [Line Items]
Net sales:	191,110	190,247	346,157	350,853
Point in Time | Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	130,958	127,252	233,842	231,803
Point in Time | Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	51,428	57,612	97,971	107,874
Point in Time | Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	8,724	5,383	14,344	11,176
Over Time
Disaggregation of Revenue [Line Items]
Net sales:	74,926	57,380	135,216	103,379
Over Time | Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	170	0	1,234	0
Over Time | Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	9,765	0	17,625	0
Over Time | Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	$ 64,991	$ 57,380	$ 116,357	$ 103,379

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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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Publisher FASB
-Name Accounting Standards Codification
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