Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Net sales:	$ 262,655	$ 266,036	$ 490,072	$ 481,373
Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	130,433	131,128	234,142	235,076
Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	56,218	61,193	111,089	115,596
Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	76,004	73,715	144,841	130,701
Point in Time
Disaggregation of Revenue [Line Items]
Net sales:	184,350	191,110	339,819	346,157
Point in Time | Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	129,566	130,958	232,458	233,842
Point in Time | Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	46,315	51,428	91,602	97,971
Point in Time | Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	8,469	8,724	15,759	14,344
Over Time
Disaggregation of Revenue [Line Items]
Net sales:	78,305	74,926	150,253	135,216
Over Time | Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	867	170	1,684	1,234
Over Time | Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	9,903	9,765	19,487	17,625
Over Time | Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	$ 67,535	$ 64,991	$ 129,082	$ 116,357