Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)
Segment Reporting, Other Significant Reconciling Item [Line Items]
Number of reportable segments | segment			3
Net sales:	$ 262,655	$ 266,036	$ 490,072	$ 481,373
Income from operations:	63,558	70,503	107,458	118,821
Unallocated Corporate Expenses	(7,890)	(8,082)	(15,175)	(14,141)
Total consolidated income from operations	26,606	32,274	37,172	46,117
Residential Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	130,433	131,128	234,142	235,076
Income from operations:	20,778	24,196	32,868	37,434
Industrial and Infrastructure Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	56,218	61,193	111,089	115,596
Income from operations:	4,069	6,604	8,198	9,206
Renewable Energy & Conservation
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	76,004	73,715	144,841	130,701
Income from operations:	9,649	9,556	11,281	13,618
Operating Segments | Residential Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	130,433	131,128
Operating Segments | Industrial and Infrastructure Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	56,547	61,561
Intersegment Elimination
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:	$ (329)	$ (368)	(646)	(589)
Intersegment Elimination | Industrial and Infrastructure Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:			$ 111,735	$ 116,185