Segment Information (Measurements Used by Management to Assess Performance of Segments) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales	$ 258,112	$ 274,574	$ 247,627	$ 206,605	$ 231,838	$ 272,734	$ 265,738	$ 237,671	$ 986,918	$ 1,007,981	$ 1,040,873
Income (loss) from operations:	22,547	$ 35,693	$ 24,930	$ 9,679	629	$ 26,522	$ 28,576	$ 17,761	92,849	73,488	48,732
Depreciation and amortization									21,690	24,114	30,548
Total assets	991,385				918,245				991,385	918,245	889,772
Capital expenditures									11,399	10,779	12,373
Operating Segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Income (loss) from operations:									30,218	43,214	12,659
Intersegment sales
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:									(1,247)	(1,495)	(1,536)
Unallocated Corporate Expenses
Segment Reporting, Other Significant Reconciling Item [Line Items]
Income (loss) from operations:									(22,421)	(36,273)	(26,312)
Depreciation and amortization									321	377	662
Total assets	209,286				153,338				209,286	153,338	37,235
Capital expenditures									421	377	328
Residential Products | Operating Segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales									466,603	430,938	475,653
Income (loss) from operations:									76,893	65,241	46,804
Depreciation and amortization									9,183	9,297	9,967
Total assets	358,838				331,975				358,838	331,975	363,339
Capital expenditures									5,236	5,182	3,328
Industrial and Infrastructure Products
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales									213,964	295,018	376,688
Industrial and Infrastructure Products | Operating Segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales:									215,211	296,513	378,224
Income (loss) from operations:									8,159	1,306	15,581
Depreciation and amortization									6,529	8,237	12,108
Total assets	203,455				225,691				203,455	225,691	273,987
Capital expenditures									2,094	2,060	4,846
Renewable Energy & Conservation | Operating Segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net sales									306,351	282,025	188,532
Depreciation and amortization									5,657	6,203	7,811
Total assets	$ 219,806				$ 207,241				219,806	207,241	215,211
Capital expenditures									$ 3,648	$ 3,160	$ 3,871