Segments and Related Information (Schedule of Financial Information by Reportable Segment - EBITDA) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
EBITDA:
EBITDA			$ 782,500,000	$ 823,400,000	$ 660,800,000
Intangible asset, pre-tax impairment charge				3,300,000	0
Goodwill, pre-tax impairment charge					47,700,000
Loss on extinguishment of debt	$ (5,600,000)		(5,569,000)	0	0
4.875% Senior Notes [Member] | Senior Notes [Member]
EBITDA:
Loss on extinguishment of debt			5,600,000
Joint Venture [Member]
EBITDA:
Project gains (in dollars)					(1,000,000.0)
Reportable Segments [Member] | Communications [Member]
EBITDA:
EBITDA			270,100,000	208,800,000	290,400,000
Reportable Segments [Member] | Clean Energy and Infrastructure
EBITDA:
EBITDA			80,400,000	40,100,000	40,400,000
Reportable Segments [Member] | Oil and Gas [Member]
EBITDA:
EBITDA			510,900,000	634,200,000	451,600,000
Reportable Segments [Member] | Electrical Transmission [Member]
EBITDA:
EBITDA			14,900,000	29,500,000	10,500,000
Reportable Segments [Member] | Other [Member]
EBITDA:
EBITDA			30,700,000	26,500,000	24,400,000
Corporate [Member]
EBITDA:
EBITDA			$ (124,500,000)	(115,700,000)	$ (156,400,000)
Pre-Qualifications [Member]
EBITDA:
Intangible asset, pre-tax impairment charge		$ 3,300,000		$ 3,300,000