Segments and Related Information (Schedule of Financial Information by Reportable Segment - Revenue) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue:
Revenue (in dollars)		$ 1,939,006	$ 1,617,804	$ 3,457,346	$ 3,014,638
Communications [Member] | Customer Concentration Risk [Member] | Revenue [Member] | Utilities [Member]
Revenue:
Utilities customers, percentage of Communications segment revenue		15.40%	13.60%	15.50%	15.70%
Reportable Segments [Member] | Communications [Member]
Revenue:
Revenue (in dollars)	[1]	$ 652,600	$ 618,600	$ 1,265,400	$ 1,245,700
Reportable Segments [Member] | Oil and Gas [Member]
Revenue:
Revenue (in dollars)		936,800	769,300	1,558,100	1,305,800
Reportable Segments [Member] | Electrical Transmission [Member]
Revenue:
Revenue (in dollars)		100,400	84,500	195,300	198,500
Reportable Segments [Member] | Power Generation and Industrial [Member]
Revenue:
Revenue (in dollars)		250,200	146,000	439,600	263,600
Reportable Segments [Member] | Other [Member]
Revenue:
Revenue (in dollars)		0	200	100	2,200
Eliminations [Member]
Revenue:
Revenue (in dollars)		$ (1,000)	$ (800)	$ (1,200)	$ (1,200)

[1] Revenue generated primarily by utilities customers represented 15.4% and 13.6% of Communications segment revenue for the three month periods ended June 30, 2019 and 2018, respectively, and represented 15.5% and 15.7% for the six month periods ended June 30, 2019 and 2018, respectively.