Segments and Related Information (Schedule of Financial Information by Reportable Segment - Capital Expenditures) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Capital Expenditures:
Capital expenditures	$ 117,114	$ 84,410	$ 109,254
Reportable Segments [Member] | Communications [Member]
Capital Expenditures:
Capital expenditures	28,500	25,800	23,400
Reportable Segments [Member] | Oil and Gas [Member]
Capital Expenditures:
Capital expenditures	64,000	38,100	44,200
Reportable Segments [Member] | Electrical Transmission [Member]
Capital Expenditures:
Capital expenditures	19,800	13,000	25,800
Reportable Segments [Member] | Power Generation and Industrial [Member]
Capital Expenditures:
Capital expenditures	3,400	3,500	6,700
Reportable Segments [Member] | Other [Member]
Capital Expenditures:
Capital expenditures	300	200	0
Corporate [Member]
Capital Expenditures:
Capital expenditures	$ 1,100	$ 3,800	$ 9,200