Segments and Related Information (Schedule of Financial Information by Reportable Segment - Depreciation and Amortization) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Depreciation and Amortization:
Depreciation and amortization	$ 49,940	$ 42,904
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	14,600	12,000
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	25,500	21,900
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	5,300	5,800
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	3,000	1,500
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	0	0
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 1,500	$ 1,700