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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Depreciation and Amortization:
Depreciation and amortization	$ 45,379	$ 40,657	$ 88,282	$ 79,664
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	13,500	12,400	25,500	24,600
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	23,200	19,300	45,100	37,500
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	5,700	5,800	11,400	11,000
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	1,400	1,500	2,900	3,100
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	$ 3,300	$ 3,500