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Segment Information - Additional information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Contract revenues	$ 571,075	$ 583,214	$ 448,776	$ 468,094	$ 446,345	$ 399,537	$ 339,676	$ 345,611	$ 2,071,159	$ 1,531,169	$ 1,403,317
Identifiable assets	1,007,871				748,755				$ 1,007,871	748,755
Number of business segments (segment) | segment									2
C&I [Member]
Segment Reporting Information [Line Items]
Contract revenues									$ 936,748	638,061	523,945
Identifiable assets	414,264				257,049				414,264	257,049
CANADA
Segment Reporting Information [Line Items]
Identifiable assets	$ 24,800				$ 20,500				24,800	20,500
CANADA | C&I [Member]
Segment Reporting Information [Line Items]
Contract revenues									$ 79,500	$ 53,800	$ 84,100

X

- Definition

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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