Segments and Related Information (Schedule of Financial Information by Reportable Segment - EBITDA) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
EBITDA:
EBITDA		$ 46,200	$ 42,800
Equity in earnings (losses) of unconsolidated affiliates		3,066	(585)
Oil and Gas [Member]
EBITDA:
Equity in earnings (losses) of unconsolidated affiliates		3,600	(600)
Other [Member]
EBITDA:
Equity in earnings (losses) of unconsolidated affiliates		(500)
Reportable Segments [Member] | Communications [Member]
EBITDA:
EBITDA		61,700	51,700
Reportable Segments [Member] | Oil and Gas [Member]
EBITDA:
EBITDA	[1]	16,200	21,500
Reportable Segments [Member] | Electrical Transmission [Member]
EBITDA:
EBITDA		(23,800)	(2,500)
Reportable Segments [Member] | Power Generation and Industrial [Member]
EBITDA:
EBITDA		2,900	(8,900)
Reportable Segments [Member] | Other [Member]
EBITDA:
EBITDA	[2]	200	(5,100)
Corporate [Member]
EBITDA:
EBITDA		$ (11,000)	$ (13,900)

[1] Oil and Gas EBITDA includes equity in earnings from unconsolidated affiliates of $3.6 million for the three month period ended March 31, 2016, and equity in losses from unconsolidated affiliates of $0.6 million for the three month period ended March 31, 2015.

[2] Other EBITDA includes equity in losses from unconsolidated affiliates of $0.5 million for the three month period ended March 31, 2016.