Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Revenue Recognition [Line Items]
Revenues recognized related to change orders and claims	$ 122,800		$ 121,800
Percent of total revenues recognized associated with revenue recognition method	49.00%	54.20%
Revenue recognized related to amounts in contract liabilities outstanding at the beginning of period	$ 262,000	$ 264,000
Revenue, related to performance obligation satisfied in previous periods	17,000	26,000
Allowances for doubtful accounts on current receivables	8,476		5,839
Long-term accounts receivable	69,000		25,900
Current retainage balances	467,500		337,100
Non-current retainage balances	8,600		99,600
Unbilled receivables	481,300		434,900
Unearned revenues included in accounts payable and accrued expenses	1,238,727		1,314,520
Unearned Revenue
Revenue Recognition [Line Items]
Unearned revenues included in accounts payable and accrued expenses	28,800		$ 40,100
EPC Electric Transmission Project
Revenue Recognition [Line Items]
Change in contract estimates, favorable (unfavorable) impact on operating results	25,500	$ 16,800
PG&E
Revenue Recognition [Line Items]
Long-term accounts receivable	$ 41,200

Contract With Customer, Cumulative Catch-Up Adjustment To Gross Profit, Change In Estimate

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Revenue From Contract With Customer, Percentage Of Revenue Recognized Over Time

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Revenue Recognized, Related To Unapproved Change Orders And Claims

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Sum of the carrying values as of the balance sheet date of obligations incurred through that date and due within one year (or the operating cycle, if longer), including liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received, taxes, interest, rent and utilities, accrued salaries and bonuses, payroll taxes and fringe benefits.

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Amount due from customers or clients, more than one year from the balance sheet date, for goods or services that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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Amount billed to customers under long-term contracts or programs that have been withheld because of retainage provisions in a contract to be collected after the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of revenue recognized from performance obligation satisfied or partially satisfied in previous reporting periods. Includes, but is not limited to, change in transaction price.

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