Segment Information - Additional information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Contract revenues	$ 513,051	$ 448,776	$ 1,031,521	$ 916,870
Number of business segments (segment) | segment			2
C&I [Member]
Segment Reporting Information [Line Items]
Contract revenues	236,292	192,866	$ 495,492	388,412
C&I [Member] | CANADA
Segment Reporting Information [Line Items]
Contract revenues	$ 20,900	$ 20,800	$ 39,000	$ 33,500