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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

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