Goodwill and Other Intangible Assets (2018 Acquisitions) (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earn-Out Liabilities [Member]
Business Combinations [Line Items]
Additions to acquisition-related contingent consideration	$ 4,161	$ 0
2018 Acquisitions [Member]
Business Combinations [Line Items]
Business combinations, percentage of interests acquired	100.00%
Business combinations, cash paid (in dollars)	$ 6,100
2018 Acquisitions [Member] | Earn-Out Liabilities [Member]
Business Combinations [Line Items]
Additions to acquisition-related contingent consideration	$ 1,500
2018 Power Generation and Industrial Acquisition A [Member]
Business Combinations [Line Items]
Business combinations, description of acquired entity	a construction management firm specializing in steel building systems
2018 Power Generation and Industrial Acquisition B [Member]
Business Combinations [Line Items]
Business combinations, description of acquired entity	a wind turbine services company