Segments and Related Information (Schedule of Financial Information by Reportable Segment - Depreciation and Amortization) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Depreciation and Amortization:
Depreciation and amortization	$ 50,101	$ 42,584	$ 138,384	$ 122,249
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	13,800	12,500	39,400	37,200
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	26,000	20,700	71,100	58,200
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	5,800	6,100	17,300	17,100
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	2,900	1,600	5,800	4,600
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	0	0	100	0
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 1,600	$ 1,700	$ 4,700	$ 5,100