Goodwill and Related Intangible Assets (Schedule of Changes in Carrying Amount of Goodwill) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Balance at	$ 304,032,000	$ 292,390,000
Acquired goodwill	16,790,000	12,283,000
Adjustments to prior year acquisitions	(832,000)
Impairment	0	(929,000)
Foreign currency translation	1,084,000	288,000
Balance at	321,074,000	304,032,000
Residential Products
Goodwill [Roll Forward]
Balance at	181,285,000	181,285,000
Acquired goodwill	16,790,000	0
Adjustments to prior year acquisitions	0
Impairment		0
Foreign currency translation	0	0
Balance at	198,075,000	181,285,000
Industrial and Infrastructure Products
Goodwill [Roll Forward]
Balance at	53,884,000	53,704,000
Acquired goodwill	0	0
Adjustments to prior year acquisitions	0
Impairment		0
Foreign currency translation	396,000	180,000
Balance at	54,280,000	53,884,000
Renewable Energy & Conservation
Goodwill [Roll Forward]
Balance at	68,863,000	57,401,000
Acquired goodwill	0	12,283,000
Adjustments to prior year acquisitions	(832,000)
Impairment		(929,000)
Foreign currency translation	688,000	108,000
Balance at	$ 68,719,000	$ 68,863,000