Segments and Related Information (Schedule of Financial Information by Reportable Segment - Revenue) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Revenue (in dollars)		$ 1,602,900	$ 1,955,800	$ 1,890,200	$ 1,158,200	$ 1,341,900	$ 1,586,200	$ 1,232,400	$ 974,200	$ 6,606,978	$ 5,134,703	$ 4,208,330
Communications [Member] | Customer Concentration Risk [Member] | Revenue [Member] | Utilities [Member]
Revenue:
Utilities customers, percentage of Communications segment revenue										13.40%	11.10%	10.60%
Reportable Segments [Member] | Communications [Member]
Revenue:
Revenue (in dollars)	[1]									$ 2,424,400	$ 2,323,600	$ 1,973,200
Reportable Segments [Member] | Oil and Gas [Member]
Revenue:
Revenue (in dollars)										3,497,200	2,024,400	1,495,100
Reportable Segments [Member] | Electrical Transmission [Member]
Revenue:
Revenue (in dollars)										378,200	383,800	341,500
Reportable Segments [Member] | Power Generation and Industrial [Member]
Revenue:
Revenue (in dollars)										299,900	405,700	381,600
Reportable Segments [Member] | Other [Member]
Revenue:
Revenue (in dollars)										20,800	15,900	24,100
Eliminations [Member]
Revenue:
Revenue (in dollars)										$ (13,500)	$ (18,700)	$ (7,200)

[1] Revenue generated primarily by utilities customers represented 13.4%, 11.1% and 10.6% of Communications segment revenue for the years ended December 31, 2017, 2016 and 2015, respectively.