Segments and Related Information (Schedule of Financial Information by Reportable Segment - Depreciation and Amortization) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Depreciation and Amortization:
Depreciation and amortization	$ 235,482	$ 212,930	$ 188,049
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	65,000	59,300	53,200
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	127,200	113,700	96,700
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	20,000	19,800	22,800
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	14,100	13,700	9,100
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	100	100	100
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 9,100	$ 6,300	$ 6,100