Segments and Related Information (Schedule of Financial Information by Reportable Segment - Revenue) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue:
Revenue (in dollars)		$ 1,617,804	$ 1,890,180	$ 3,014,638	$ 3,048,364
Communications [Member] | Customer Concentration Risk [Member] | Revenue [Member] | Utilities [Member]
Revenue:
Utilities customers, percentage of Communications segment revenue		13.60%	11.50%	15.70%	12.40%
Reportable Segments [Member] | Communications [Member]
Revenue:
Revenue (in dollars)	[1]	$ 618,600	$ 592,200	$ 1,245,700	$ 1,151,700
Reportable Segments [Member] | Oil and Gas [Member]
Revenue:
Revenue (in dollars)		769,300	1,140,400	1,305,800	1,596,200
Reportable Segments [Member] | Electrical Transmission [Member]
Revenue:
Revenue (in dollars)		84,500	96,600	198,500	195,400
Reportable Segments [Member] | Power Generation and Industrial [Member]
Revenue:
Revenue (in dollars)		146,000	60,700	263,600	107,300
Reportable Segments [Member] | Other [Member]
Revenue:
Revenue (in dollars)		200	1,900	2,200	3,600
Eliminations [Member]
Revenue:
Revenue (in dollars)		$ (800)	$ (1,600)	$ (1,200)	$ (5,800)

[1] Revenue generated primarily by utilities customers represented 13.6% and 11.5% of Communications segment revenue for the three month periods ended June 30, 2018 and 2017, respectively, and represented 15.7% and 12.4% for the six month periods ended June 30, 2018 and 2017, respectively.