Segments and Related Information (Schedule of Financial Information by Reportable Segment - Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets:
Assets	$ 3,563,980	$ 3,465,901	$ 3,388,828	$ 3,005,466	$ 2,923,198	$ 2,416,300
Continuing Operations [Member]
Assets:
Assets	3,564,000				2,910,700	2,390,100
Reportable Segments [Member] | Communications [Member]
Assets:
Assets	1,197,400				973,500	843,500
Reportable Segments [Member] | Oil and Gas [Member]
Assets:
Assets	1,389,500				1,060,800	809,200
Reportable Segments [Member] | Electrical Transmission [Member]
Assets:
Assets	489,500				449,300	311,200
Reportable Segments [Member] | Power Generation and Industrial [Member]
Assets:
Assets	340,100				324,500	323,800
Reportable Segments [Member] | Other [Member]
Assets:
Assets	24,600				22,800	6,900
Corporate [Member]
Assets:
Assets	$ 122,900				$ 79,800	$ 95,500