Business, Basis of Presentation and Significant Accounting Policies (Goodwill and Indefinite-Lived Intangible Assets) (Narrative) (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($) yr	Dec. 31, 2020 USD ($) yr component reportingunit	Dec. 31, 2019 USD ($) yr reportingunit component	Dec. 31, 2018 USD ($) reportingunit component
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Goodwill, carrying amount (in dollars)	$ 1,221,440,000	$ 1,243,034,000	$ 1,221,440,000	$ 1,100,400,000
Intangible asset, pre-tax impairment charge			3,300,000	0
Goodwill, pre-tax impairment charge				47,700,000
Pre-Qualifications [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Intangible asset, pre-tax impairment charge	3,300,000		3,300,000
Indefinite-lived intangible assets, carrying amount (in dollars)	$ 72,900,000	$ 0	$ 72,900,000	$ 74,000,000.0
Goodwill [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Discount rate sensitivity analysis, spread on discount rate for which evaluation was completed (percentage)		1.00%	1.00%
Terminal Growth Rate [Member] | Minimum [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Goodwill impairment testing, measurement input	0.030	0.025	0.030
Number of Years of Discounted Cash Flows [Member] | Minimum [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Goodwill impairment testing, measurement input | yr	5	5	5
Number of Years of Discounted Cash Flows [Member] | Maximum [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Goodwill impairment testing, measurement input | yr	9	9	9
Number of Years of Discounted Cash Flows [Member] | Maximum [Member] | Pre-Qualifications [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets, impairment testing, measurement input | yr	4		4
Discount Rate [Member] | Pre-Qualifications [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets, impairment testing, measurement input	0.13		0.13
Discount Rate [Member] | Minimum [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Goodwill impairment testing, measurement input	0.130	0.130	0.130
Discount Rate [Member] | Maximum [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Goodwill impairment testing, measurement input	0.160	0.150	0.160
Clean Energy and Infrastructure
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Number of aggregated components in reporting unit | component		2	2	2
Goodwill, carrying amount (in dollars)	$ 152,600,000	$ 152,700,000	$ 152,600,000	$ 143,100,000
Communications [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Number of aggregated components in reporting unit | component		1	1	1
Goodwill impairment testing, number of reporting units | reportingunit		1	1	2
Goodwill, carrying amount (in dollars)	541,300,000	$ 562,100,000	$ 541,300,000	$ 467,800,000
Oil and Gas [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Number of aggregated components in reporting unit | component		1	1	1
Goodwill impairment testing, number of reporting units | reportingunit		3	3	3
Goodwill, carrying amount (in dollars)	377,600,000	$ 378,100,000	$ 377,600,000	$ 339,600,000
Oil and Gas [Member] | Pre-Qualifications [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets, carrying amount (in dollars)	41,400,000		$ 41,400,000
Oil and Gas [Member] | Reporting Unit A, Quantitative Testing [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Goodwill impairment testing, number of reporting units | reportingunit		3	1	1
Oil and Gas [Member] | Reporting Unit B, Quantitative Testing [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Goodwill impairment testing, number of reporting units | reportingunit			2
Goodwill, carrying amount (in dollars)	$ 15,000,000.0		$ 15,000,000.0
Goodwill impairment testing, reporting unit, percentage of estimated fair value in excess of carrying value	15.00%		15.00%
Electrical Transmission [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Percentage of aggregated components in reporting unit		100.00%	100.00%	100.00%
Goodwill, carrying amount (in dollars)	$ 149,900,000	$ 150,100,000	$ 149,900,000	$ 149,900,000
Other [Member]
Goodwill and Indefinite-Lived Intangible Assets [Line Items]
Number of aggregated components in reporting unit | component		1	1	1