Goodwill and Related Intangible Assets (Schedule of Changes in Carrying Amount of Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Balance at	$ 323,671	$ 321,074
Acquired goodwill	5,857	3,051
Adjustments to prior year acquisitions	(172)	(38)
Foreign currency translation	349	(416)
Balance at	329,705	323,671
Renewable Energy & Conservation
Goodwill [Roll Forward]
Balance at	71,827	68,719
Acquired goodwill	5,857	3,051
Adjustments to prior year acquisitions	(172)	0
Foreign currency translation	90	57
Balance at	77,602	71,827
Residential Products
Goodwill [Roll Forward]
Balance at	198,075	198,075
Acquired goodwill	0	0
Adjustments to prior year acquisitions	0	0
Foreign currency translation	0	0
Balance at	198,075	198,075
Industrial and Infrastructure Products
Goodwill [Roll Forward]
Balance at	53,769	54,280
Acquired goodwill	0	0
Adjustments to prior year acquisitions	0	(38)
Foreign currency translation	259	(473)
Balance at	$ 54,028	$ 53,769