Segments and Related Information (Schedule of Financial Information by Reportable Segment - Depreciation and Amortization) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Depreciation and Amortization:
Depreciation and amortization	$ 43,254	$ 36,755	$ 85,852	$ 70,249
Reportable Segments [Member] | Communications [Member]
Depreciation and Amortization:
Depreciation and amortization	12,400	10,000	24,400	19,900
Reportable Segments [Member] | Oil and Gas [Member]
Depreciation and Amortization:
Depreciation and amortization	22,300	19,900	44,300	38,000
Reportable Segments [Member] | Electrical Transmission [Member]
Depreciation and Amortization:
Depreciation and amortization	5,200	3,900	10,500	6,700
Reportable Segments [Member] | Power Generation and Industrial [Member]
Depreciation and Amortization:
Depreciation and amortization	1,700	1,600	3,300	3,100
Reportable Segments [Member] | Other [Member]
Depreciation and Amortization:
Depreciation and amortization	0	0	0	0
Corporate [Member]
Depreciation and Amortization:
Depreciation and amortization	$ 1,700	$ 1,400	$ 3,400	$ 2,500