Segments and Related Information (Schedule of Financial Information by Reportable Segment - Capital Expenditures) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Capital Expenditures:
Capital expenditures	$ 126,473	$ 180,420	$ 123,412
Reportable Segments [Member] | Communications [Member]
Capital Expenditures:
Capital expenditures	36,000	69,300	40,500
Reportable Segments [Member] | Oil and Gas [Member]
Capital Expenditures:
Capital expenditures	59,700	83,500	57,700
Reportable Segments [Member] | Electrical Transmission [Member]
Capital Expenditures:
Capital expenditures	6,800	10,200	14,900
Reportable Segments [Member] | Power Generation and Industrial [Member]
Capital Expenditures:
Capital expenditures	12,700	6,500	5,400
Reportable Segments [Member] | Other [Member]
Capital Expenditures:
Capital expenditures	0	0	0
Corporate [Member]
Capital Expenditures:
Capital expenditures	$ 11,300	$ 10,900	$ 4,900