Segments and Related Information (Schedule of Financial Information by Reportable Segment - Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets:
Assets	$ 4,997,006	$ 4,439,953	$ 4,066,600
Reportable Segments [Member] | Communications [Member]
Assets:
Assets	1,958,100	1,461,700	1,314,400
Reportable Segments [Member] | Oil and Gas [Member]
Assets:
Assets	1,762,400	1,965,300	1,762,600
Reportable Segments [Member] | Electrical Transmission [Member]
Assets:
Assets	463,900	423,900	471,400
Reportable Segments [Member] | Power Generation and Industrial [Member]
Assets:
Assets	570,500	358,700	288,600
Reportable Segments [Member] | Other [Member]
Assets:
Assets	192,200	193,900	153,200
Corporate [Member]
Assets:
Assets	$ 49,900	$ 36,500	$ 76,400