Revenue from Contracts with Customers (Details) - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Cumulative effect on retained earnings, net of tax	[1]	$ 854,000
Performance obligation satisfied in previous period		7,300,000	$ 18,100,000
Change in estimate of transaction price		0	0
Loss on contracts			0
Unbilled revenues for unapproved change orders		25,200,000	17,400,000
Accounts receivable, unapproved contract claims		0	0
Accounts receivable, contractually billed amounts on contracts related to unapproved contract claims		96,100,000	57,600,000
Net billings in excess of costs		359,157,000	401,535,000
Change in net contract liabilities		52,700,000
Change in net billings in excess of costs		42,400,000
Contract asset impairment		0
Accounts receivable, retainage		$ 254,600,000	243,500,000
Accounts receivable, retainage estimated to be collected in next fiscal year		86.00%
Accounts payable, retainage		$ 43,300,000	$ 41,000,000
Accounts payable, retainage estimated to be paid in next fiscal year		83.00%
Remaining performance obligations		$ 3,964,282,000
2018 Acquisitions
Business Acquisition [Line Items]
Increase (decrease) in contract assets from acquisitions		3,800,000
Increase (decrease) in contract liabilities from acquisitions		9,400,000
United States Electrical Construction And Facilities Services | Transportation Sector [Member]
Business Acquisition [Line Items]
Loss on contracts		10,000,000		$ 19,400,000
Accounting Standards Update 2014-09 [Member]
Business Acquisition [Line Items]
Cumulative effect on retained earnings, net of tax		$ 900,000

[1] Represents adjustment to retained earnings upon the adoption of Accounting Standards Codification Topic 606.