Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	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