Summary of Significant Accounting Policies - Revenue Recognition (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue Recognition [Line Items]
Revenue recognized related to amounts in contract liabilities outstanding at the beginning of period	$ 79,000		$ 343,000
Revenue, remaining performance obligation	$ 5,580,000		$ 5,580,000
Revenue, remaining performance obligation expected to be recognized within twelve months	79.80%		79.80%
Change orders and/or claims	$ 110,600		$ 110,600			$ 144,000
Revenue, related to performance obligation satisfied in previous periods	15,800		47,400
Change in contract estimates, impact on operating results, gain (loss)	$ 800	$ 28,800	$ 14,200	$ 31,000
Percent aggregate change in contract estimates impact on gross margin	0.20%	9.50%	2.20%	5.50%
Accounts payable and accrued expenses	$ 1,178,983		$ 1,178,983			1,057,460
EPC Electric Transmission Project
Revenue Recognition [Line Items]
Change in contract estimates, impact on operating results, gain (loss)	16,600		26,300
Natural Gas Transmission Project
Revenue Recognition [Line Items]
Change in contract estimates, impact on operating results, gain (loss)		$ 24,600
Retained Earnings | Accounting Standards Update 2014-09
Revenue Recognition [Line Items]
Cumulative effect adjustment					$ (1,800)
Unearned Revenue
Revenue Recognition [Line Items]
Accounts payable and accrued expenses	$ 11,400		$ 11,400			$ 16,000