Summary of Significant Accounting Policies - Revenue Recognition (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ 2,425,832,000		$ 2,425,832,000			$ 2,191,059,000
Remaining performance obligation	5,290,000,000		5,290,000,000
Revenues recognized related to change orders and claims	118,300,000		118,300,000			144,000,000.0
Revenue, related to performance obligation satisfied in previous periods	47,200,000		71,000,000.0
Change in contract estimates, favorable (unfavorable) impact on operating results	$ 30,700,000	$ (2,800,000)	$ (4,600,000)	$ 24,400,000
Percent aggregate change in contract estimates impact on gross margin	7.20%	(0.80%)	(0.40%)	2.70%
Revenue recognized related to amounts in contract liabilities outstanding at the beginning of period	$ 32,000,000		$ 375,000,000
Accounts payable and accrued expenses	1,340,882,000		1,340,882,000			1,057,460,000
EPC Electric Transmission Project
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Change in contract estimates, favorable (unfavorable) impact on operating results	47,100,000		47,200,000
$150 Million Lump-Sum Processing Facility Construction Project
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Change in contract estimates, favorable (unfavorable) impact on operating results	$ (18,800,000)		$ (20,600,000)
Percentage of completion	82.00%		82.00%
Lump-sum amount	$ 150,000,000		$ 150,000,000
$145 Million Lump Sum Natural Gas Pipeline Construction Project
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Change in contract estimates, favorable (unfavorable) impact on operating results	(10,800,000)		(7,600,000)
$50 Million Lump Sum Natural Gas Pipeline Construction Project
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Change in contract estimates, favorable (unfavorable) impact on operating results	$ (6,200,000)		$ (16,400,000)
Percentage of completion	98.00%		98.00%
Lump-sum amount	$ 50,000,000		$ 50,000,000
Unearned Revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts payable and accrued expenses	$ 20,000,000.0		$ 20,000,000.0			$ 16,000,000.0
Accounting Standards Update 2014-09 | Adjustment Due to Adoption of New Guidance
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings					$ (1,800,000)