Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Net sales:	$ 227,417	$ 215,337
Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	103,709	103,948
Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	54,871	54,403
Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	68,837	56,986
Point in Time
Disaggregation of Revenue [Line Items]
Net sales:	155,469	155,047
Point in Time | Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	102,892	102,884
Point in Time | Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	45,287	46,543
Point in Time | Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	7,290	5,620
Over Time
Disaggregation of Revenue [Line Items]
Net sales:	71,948	60,290
Over Time | Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	817	1,064
Over Time | Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	9,584	7,860
Over Time | Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	$ 61,547	$ 51,366