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Goodwill and Related Intangible Assets (Narrative) (Details) |  | 12 Months Ended
--- | --- | ---
Oct. 31, 2017 reporting_unit | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Goodwill [Line Items] |  |  |  |
Goodwill |  | $ 321,074,000 | $ 304,032,000 | $ 292,390,000
Accumulated impairment losses |  | 235,400,000 | 255,530,000 |
Number of reporting units tested | reporting_unit | 11 |  |  |
Goodwill impairment |  | 0 | (929,000) |
Impairment of indefinite-lived intangibles |  | 247,000 | 9,048,000 | 4,863,000
Impairment of definite-lived intangibles |  | 0 | 198,000 | 0
Industrial and Infrastructure Products |  |  |  |
Goodwill [Line Items] |  |  |  |
Impairment of indefinite-lived intangibles |  | 0 | 7,980,000 | 4,423,000
Impairment of definite-lived intangibles |  | 0 | 0 | 0
Residential Products |  |  |  |
Goodwill [Line Items] |  |  |  |
Impairment of indefinite-lived intangibles |  | 0 | 0 | 440,000
Impairment of definite-lived intangibles |  | 0 | $ 0 | $ 0
Solar | Residential Products |  |  |  |
Goodwill [Line Items] |  |  |  |
Goodwill impairment |  | $ (900,000) |  |

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975 + Details
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- Definition Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a,h) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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