Segments and Related Information (Schedule of Financial Information by Reportable Segment - Revenue) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue:
Revenue (in dollars)		$ 1,977,227	$ 1,955,752	$ 4,991,865	$ 5,004,116
Communications [Member] | Customer Concentration Risk [Member] | Revenue [Member] | Utilities [Member]
Revenue:
Utilities customers, percentage of Communications segment revenue		13.90%	13.00%	15.10%	12.60%
Reportable Segments [Member] | Communications [Member]
Revenue:
Revenue (in dollars)	[1]	$ 661,700	$ 610,500	$ 1,907,500	$ 1,762,200
Reportable Segments [Member] | Oil and Gas [Member]
Revenue:
Revenue (in dollars)		1,035,900	1,161,000	2,341,600	2,757,200
Reportable Segments [Member] | Electrical Transmission [Member]
Revenue:
Revenue (in dollars)		99,100	81,800	297,600	277,300
Reportable Segments [Member] | Power Generation and Industrial [Member]
Revenue:
Revenue (in dollars)		179,600	96,900	443,200	204,100
Reportable Segments [Member] | Other [Member]
Revenue:
Revenue (in dollars)		1,600	10,600	3,700	14,200
Eliminations [Member]
Revenue:
Revenue (in dollars)		$ (700)	$ (5,000)	$ (1,700)	$ (10,900)

[1] Revenue generated primarily by utilities customers represented 13.9% and 13.0% of Communications segment revenue for the three month periods ended September 30, 2018 and 2017, respectively, and represented 15.1% and 12.6% for the nine month periods ended September 30, 2018 and 2017, respectively.