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Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)
Segment Reporting, Other Significant Reconciling Item [Line Items]
Number of reportable segments | segment			3
Net sales:	$ 266,036	$ 247,627	$ 481,373	$ 454,232
Income from operations:	70,503	61,825	118,821	111,080
Unallocated Corporate Expenses	(8,082)	(4,538)	(14,141)	(13,803)
Total income from operations	32,274	24,930	46,117	34,609
Residential Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	131,128	127,252	235,076	231,803
Income from operations:	24,196	22,579	37,434	38,220
Industrial and Infrastructure Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	61,193	57,612	115,596	107,874
Income from operations:	6,604	3,397	9,206	3,360
Renewable Energy & Conservation
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	73,715	62,763	130,701	114,555
Income from operations:	9,556	3,492	13,618	6,832
Intersegment Elimination
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	(368)	(314)	(589)	(770)
Intersegment Elimination | Industrial and Infrastructure Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	$ 61,561	$ 57,926	$ 116,185	$ 108,644

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