Segments and Related Information (Schedule of Financial Information by Reportable Segment - Depreciation and Amortization) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Depreciation and Amortization:
Depreciation and amortization	$ 59,944	$ 51,676	$ 118,975	$ 101,615
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	15,300	15,300	30,000	29,900
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	34,300	26,100	68,900	51,600
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	5,200	5,100	9,700	10,400
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	3,300	3,600	6,400	6,600
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	0	0	0	100
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 1,800	$ 1,600	$ 4,000	$ 3,000