Segments and Related Information (Schedule of Financial Information by Reportable Segment - Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets:
Assets	$ 5,227,849	$ 4,997,006	$ 4,440,000
Reportable Segments [Member] | Communications [Member]
Assets:
Assets	1,941,900	1,958,100	1,461,700
Reportable Segments [Member] | Clean Energy and Infrastructure
Assets:
Assets	653,700	570,500	358,700
Reportable Segments [Member] | Oil and Gas [Member]
Assets:
Assets	1,631,100	1,762,400	1,965,300
Reportable Segments [Member] | Electrical Transmission [Member]
Assets:
Assets	541,600	463,900	423,900
Reportable Segments [Member] | Other [Member]
Assets:
Assets	191,800	192,200	193,900
Corporate [Member]
Assets:
Assets	$ 267,700	$ 49,900	$ 36,500