Segments and Related Information (Schedule of Financial Information by Reportable Segment - Depreciation and Amortization) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Depreciation and Amortization:
Depreciation and amortization	$ 55,196	$ 54,863	$ 174,171	$ 156,478
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	15,700	14,500	45,700	44,400
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	28,800	30,600	97,700	82,100
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	5,100	4,800	14,800	15,200
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	3,300	3,400	9,700	9,900
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	0	0	100	100
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 2,300	$ 1,600	$ 6,200	$ 4,800