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Goodwill and Related Intangible Assets (Tables) | 12 Months Ended
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Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract] |
Schedule of Changes in Carrying Amount of Goodwill | The changes in the carrying amount of goodwill for the years ended December 31 were as follows (in thousands):
| Residential Products |  | Industrial and Infrastructure Products |  | Renewable Energy and Conservation |  | Total
Balance at December 31, 2015 | $ | 181,285 |  |  | $ | 53,704 |  |  | $ | 57,401 |  |  | $ | 292,390 |
Acquired goodwill | — |  |  | — |  |  | 12,283 |  |  | 12,283 |
Impairment | — |  |  | — |  |  | (929 | ) |  | (929 | )
Foreign currency translation | — |  |  | 180 |  |  | 108 |  |  | 288 |
Balance at December 31, 2016 | $ | 181,285 |  |  | $ | 53,884 |  |  | $ | 68,863 |  |  | $ | 304,032 |
Acquired goodwill | 16,790 |  |  | — |  |  | — |  |  | 16,790 |
Adjustments to prior year acquisitions | — |  |  | — |  |  | (832 | ) |  | (832 | )
Foreign currency translation | — |  |  | 396 |  |  | 688 |  |  | 1,084 |
Balance at December 31, 2017 | $ | 198,075 |  |  | $ | 54,280 |  |  | $ | 68,719 |  |  | $ | 321,074 |
Schedule of Acquired Intangible Assets | Acquired intangible assets consist of the following (in thousands):
| December 31, 2017 |  | December 31, 2016 |  |
| Gross Carrying Amount |  | Accumulated Amortization |  | Gross Carrying Amount |  | Accumulated Amortization |  | Estimated Useful Life
Indefinite-lived intangible assets: |  |  |  |  |  |  |  |  |
Trademarks | $ | 45,107 |  |  | $ | — |  |  | $ | 44,720 |  |  | $ | — |  |  | Indefinite
Finite-lived intangible assets: |  |  |  |  |  |  |  |  |
Trademarks | 5,876 |  |  | 3,062 |  |  | 5,808 |  |  | 2,427 |  |  | 5 to 15 Years
Unpatented technology | 28,107 |  |  | 12,033 |  |  | 26,720 |  |  | 10,041 |  |  | 5 to 20 Years
Customer relationships | 80,707 |  |  | 39,652 |  |  | 78,569 |  |  | 33,585 |  |  | 5 to 17 Years
Non-compete agreements | 1,649 |  |  | 931 |  |  | 1,649 |  |  | 623 |  |  | 4 to 10 Years
Backlog | — |  |  | — |  |  | 900 |  |  | 900 |  |  | .5 to 2 Years
| 116,339 |  |  | 55,678 |  |  | 113,646 |  |  | 47,576 |  |  |
Total acquired intangible assets | $ | 161,446 |  |  | $ | 55,678 |  |  | $ | 158,366 |  |  | $ | 47,576 |  |  |
Schedule of Acquired Intangible Asset Amortization Expense | The following table summarizes the impairment charges for the years ended December 31 (in thousands):
| 2017 |  | 2016 |  | 2015
| Indefinite-lived intangibles (1) |  | Definite-lived intangibles |  | Indefinite-lived intangibles (2) |  | Definite-lived intangibles (3) |  | Indefinite-lived intangibles (4) |  | Definite-lived intangibles
Residential Products | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 440 |  |  | $ | — |
Industrial and Infrastructure Products | — |  |  | — |  |  | 7,980 |  |  | — |  |  | 4,423 |  |  | — |
Renewable Energy and Conservation | 247 |  |  | — |  |  | 1,068 |  |  | 198 |  |  | — |  |  | — |
Impairment charges | $ | 247 |  |  | $ | — |  |  | $ | 9,048 |  |  | $ | 198 |  |  | $ | 4,863 |  |  | $ | — |
(1) Renewable Energy and Conservation impairment charges due to the discontinuation of its domestic greenhouse business in China. (2) Industrial and Infrastructure Products impairment charges due to discontinuation of U.S. bar grating product line and annual testing. Renewable Energy and Conservation impairment due to discontinuation of European residential solar racking business and annual testing. (3) Renewable Energy and Conservation impairment due to discontinuation of European residential solar racking business. (4) 2015 impairment charges recognized as a result of the Company’s annual impairment test of indefinite-lived intangibles.
Schedule of Intangible Assets Amortization Expense | The following table summarizes amortization expense for the years ended December 31 (in thousands):
| 2017 |  | 2016 |  | 2015
Amortization expense | $ | 8,761 |  |  | $ | 9,637 |  |  | $ | 12,679 |
Schedule of Amortization Expense | Amortization expense related to acquired intangible assets for the next five years ended December 31 is estimated as follows (in thousands):
| 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022
Amortization expense | $ | 8,289 |  |  | $ | 7,618 |  |  | $ | 7,106 |  |  | $ | 6,504 |  |  | $ | 6,093 |

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