Summary of Significant Accounting Policies - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Loss on contracts	$ 0
Settlement of contract claim	18,100,000	$ 0
Unbilled revenues for unapproved change orders	17,400,000	21,600,000
Claims on uncompleted contracts	0	6,000,000
Accounts receivable, unapproved contract claims	0	0
Accounts receivable, contractually billed amounts on contracts related to unapproved contract claims	57,600,000	80,500,000
Accounts receivable, retainage	$ 243,500,000	222,600,000
Accounts receivable, retainage estimated to be collected in next fiscal year	85.00%
Accounts payable, retainage	$ 41,000,000	40,100,000
Accounts payable, retainage estimated to be paid in next fiscal year	88.00%
Accounts receivable, net	$ 1,607,922,000	1,495,431,000
Allowance for doubtful accounts	17,230,000	12,252,000
Provision for doubtful accounts	7,264,000	6,194,000	$ 2,853,000
Non-cash expense for impairment of property, plant and equipment	0	0	0
Non-cash goodwill impairment charge	$ 57,451,000	0	0
Minimum
Property, Plant and Equipment [Line Items]
Contract terms	1 month
Maximum
Property, Plant and Equipment [Line Items]
Contract terms	4 years
Machinery and Equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Machinery and Equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Vehicles, Furniture and Fixtures, and Computer Hardware and Software | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Vehicles, Furniture and Fixtures, and Computer Hardware and Software | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Buildings
Property, Plant and Equipment [Line Items]
Estimated useful life	25 years
United States Mechanical Construction And Facilities Services
Property, Plant and Equipment [Line Items]
Settlement of contract claim			$ 12,100,000
Non-cash goodwill impairment charge	$ 0
United States Electrical Construction And Facilities Services
Property, Plant and Equipment [Line Items]
Non-cash goodwill impairment charge	0
Other Current Liabilities
Property, Plant and Equipment [Line Items]
Insurance liabilities, current	47,300,000	42,500,000
Other Noncurrent Liabilities
Property, Plant and Equipment [Line Items]
Insurance liabilities, noncurrent	173,200,000	167,900,000
Prepaid Expenses and Other
Property, Plant and Equipment [Line Items]
Anticipated insurance recoveries, current	14,900,000	10,800,000
Other Assets
Property, Plant and Equipment [Line Items]
Anticipated insurance recoveries, noncurrent	$ 48,600,000	43,000,000
Accounting Standards Update 2015-17 [Member]
Property, Plant and Equipment [Line Items]
Cumulative effect of change on equity or net assets		41,700,000
Transportation Sector [Member] | United States Electrical Construction And Facilities Services
Property, Plant and Equipment [Line Items]
Loss on contracts		19,400,000
Manufacturing Sector [Member] | United States Mechanical Construction And Facilities Services
Property, Plant and Equipment [Line Items]
Loss on contracts		18,300,000
Institutional Sector [Member] | United States Mechanical Construction And Facilities Services
Property, Plant and Equipment [Line Items]
Loss on contracts		$ 9,600,000