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Goodwill and Related Intangible Assets (Narrative) (Details)		12 Months Ended
	Oct. 31, 2017 reporting_unit	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Goodwill [Line Items]
Goodwill		$ 323,671,000	$ 321,074,000	$ 304,032,000
Accumulated impairment losses		235,400,000	235,400,000
Number of reporting units tested | reporting_unit	12
Goodwill impairment		0
Impairment of indefinite-lived intangibles		1,237,000	247,000	9,048,000
Impairment of definite-lived intangibles		315,000	0	198,000
Industrial and Infrastructure Products
Goodwill [Line Items]
Impairment of indefinite-lived intangibles		0	0	7,980,000
Impairment of definite-lived intangibles		0	0	0
Residential Products
Goodwill [Line Items]
Impairment of indefinite-lived intangibles		200,000	0	0
Impairment of definite-lived intangibles		0	$ 0	$ 0
Solar | Residential Products
Goodwill [Line Items]
Goodwill impairment		$ (900,000)

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