Segments and Related Information (Schedule of Financial Information by Reportable Segment - Revenue) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue:
Revenue (in dollars)		$ 2,016,618	$ 1,977,227	$ 5,473,965	$ 4,991,865
Communications [Member] | Customer Concentration Risk [Member] | Revenue [Member] | Utilities [Member]
Revenue:
Utilities customers, percentage of Communications segment revenue		14.90%	13.90%	15.30%	15.10%
Reportable Segments [Member] | Communications [Member]
Revenue:
Revenue (in dollars)	[1]	$ 679,500	$ 661,700	$ 1,944,900	$ 1,907,500
Reportable Segments [Member] | Oil and Gas [Member]
Revenue:
Revenue (in dollars)		972,500	1,035,900	2,530,500	2,341,600
Reportable Segments [Member] | Electrical Transmission [Member]
Revenue:
Revenue (in dollars)		103,000	99,100	298,300	297,600
Reportable Segments [Member] | Power Generation and Industrial [Member]
Revenue:
Revenue (in dollars)		261,700	179,600	701,300	443,200
Reportable Segments [Member] | Other [Member]
Revenue:
Revenue (in dollars)		100	1,600	100	3,700
Eliminations [Member]
Revenue:
Revenue (in dollars)		$ (200)	$ (700)	$ (1,100)	$ (1,700)

[1] Revenue generated primarily by utilities customers represented 14.9% and 13.9% of Communications segment revenue for the three month periods ended September 30, 2019 and 2018, respectively, and represented 15.3% and 15.1% for the nine month periods ended September 30, 2019 and 2018, respectively.