Segment Information - Additional information (Details) $ in Thousands	3 Months Ended
Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Contract revenues	$ 518,470	$ 468,094
Number of business segments (segment) \| segment	2
C&I [Member]
Segment Reporting Information [Line Items]
Contract revenues	$ 259,200	195,546
C&I [Member] \| CANADA
Segment Reporting Information [Line Items]
Contract revenues	$ 18,100	$ 12,700

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

Name:	us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration