Segments and Related Information (Schedule of Financial Information by Reportable Segment - Depreciation and Amortization) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Depreciation and Amortization:
Depreciation and amortization	$ 42,904	$ 39,008
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	12,000	12,300
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	21,900	18,200
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	5,800	5,200
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	1,500	1,500
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	0	0
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 1,700	$ 1,800