Segments and Related Information (Schedule of Financial Information by Reportable Segment - Depreciation and Amortization) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Depreciation and Amortization:
Depreciation and amortization	$ 164,915	$ 169,662	$ 154,452
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	50,300	50,600	42,600
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	78,400	84,500	82,800
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	23,200	21,100	17,100
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	6,200	6,600	6,400
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	100	100	0
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 6,700	$ 6,800	$ 5,600