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Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)
Segment Reporting, Other Significant Reconciling Item [Line Items]
Number of reportable segments | segment			3
Net sales:	$ 280,086	$ 274,574	$ 761,459	$ 728,806
Income from operations:	70,279	68,735	189,100	179,815
Unallocated Corporate Expenses	(8,698)	(2,174)	(22,839)	(15,977)
Total income from operations	29,404	35,693	75,521	70,302
Residential Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	125,839	129,501	360,915	361,304
Income from operations:	20,138	23,764	57,572	61,984
Industrial and Infrastructure Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	55,761	56,938	171,357	164,812
Income from operations:	2,892	2,554	12,098	5,914
Renewable Energy & Conservation
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	98,486	88,135	229,187	202,690
Income from operations:	15,072	11,549	28,690	18,381
Intersegment Elimination
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	(272)	(224)	(861)	(994)
Intersegment Elimination | Industrial and Infrastructure Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	$ 56,033	$ 57,162	$ 172,218	$ 165,806

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