Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Net sales:	$ 280,086	$ 274,574	$ 761,459	$ 728,806
Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	125,839	129,501	360,915	361,304
Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	55,761	56,938	171,357	164,812
Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	98,486	88,135	229,187	202,690
Point in Time
Disaggregation of Revenue [Line Items]
Net sales:	183,588	194,098	529,745	544,951
Point in Time | Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	125,118	129,501	358,960	361,304
Point in Time | Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	47,686	56,938	145,657	164,812
Point in Time | Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	10,784	7,659	25,128	18,835
Over Time
Disaggregation of Revenue [Line Items]
Net sales:	96,498	80,476	231,714	183,855
Over Time | Residential Products
Disaggregation of Revenue [Line Items]
Net sales:	721	0	1,955	0
Over Time | Industrial and Infrastructure Products
Disaggregation of Revenue [Line Items]
Net sales:	8,075	0	25,700	0
Over Time | Renewable Energy & Conservation
Disaggregation of Revenue [Line Items]
Net sales:	$ 87,702	$ 80,476	$ 204,059	$ 183,855