Segments and Related Information (Schedule of Financial Information by Reportable Segment - Revenue) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Revenue:
Revenue (in dollars)		$ 1,518,340	$ 1,396,834
Communications [Member] | Customer Concentration Risk [Member] | Revenue [Member] | Utilities [Member]
Revenue:
Utilities customers, percentage of Communications segment revenue		15.60%	17.80%
Reportable Segments [Member] | Communications [Member]
Revenue:
Revenue (in dollars)	[1]	$ 612,800	$ 627,100
Reportable Segments [Member] | Oil and Gas [Member]
Revenue:
Revenue (in dollars)		621,300	536,500
Reportable Segments [Member] | Electrical Transmission [Member]
Revenue:
Revenue (in dollars)		94,900	114,000
Reportable Segments [Member] | Power Generation and Industrial [Member]
Revenue:
Revenue (in dollars)		189,400	117,600
Reportable Segments [Member] | Other [Member]
Revenue:
Revenue (in dollars)		0	1,900
Eliminations [Member]
Revenue:
Revenue (in dollars)		$ (100)	$ (300)

[1] Revenue generated primarily by utilities customers represented 15.6% and 17.8% of Communications segment revenue for the three month periods ended March 31, 2019 and 2018, respectively.