Segments and Related Information (Schedule of Financial Information by Reportable Segment - Depreciation and Amortization) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Depreciation and Amortization:
Depreciation and amortization	$ 59,031	$ 49,940
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	14,700	14,600
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	34,600	25,500
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	4,500	5,300
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	3,100	3,000
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	0	0
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 2,100	$ 1,500