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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Depreciation and Amortization:
Depreciation and amortization	$ 42,584	$ 42,196	$ 122,249	$ 128,048
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	12,500	13,200	37,200	37,600
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	20,700	20,000	58,200	64,300
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	6,100	5,500	17,100	16,000
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	1,600	1,700	4,600	5,000
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	0	0	0	100
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 1,700	$ 1,800	$ 5,100	$ 5,000