Segments and Related Information (Schedule of Financial Information by Reportable Segment - Revenue) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Revenue:
Revenue (in dollars)		$ 1,396,834	$ 1,158,184
Communications [Member] | Customer Concentration Risk [Member] | Revenue [Member] | Utilities [Member]
Revenue:
Utilities customers, percentage of Communications segment revenue		17.80%	13.40%
Reportable Segments [Member] | Communications [Member]
Revenue:
Revenue (in dollars)	[1]	$ 627,100	$ 559,500
Reportable Segments [Member] | Oil and Gas [Member]
Revenue:
Revenue (in dollars)		536,500	455,900
Reportable Segments [Member] | Electrical Transmission [Member]
Revenue:
Revenue (in dollars)		114,000	98,800
Reportable Segments [Member] | Power Generation and Industrial [Member]
Revenue:
Revenue (in dollars)		117,600	46,600
Reportable Segments [Member] | Other [Member]
Revenue:
Revenue (in dollars)		1,900	1,700
Eliminations [Member]
Revenue:
Revenue (in dollars)		$ (300)	$ (4,300)

[1] Revenue generated primarily by utilities customers represented 17.8% and 13.4% of Communications segment revenue for the three month periods ended March 31, 2018 and 2017, respectively.