Segment Information - Additional Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of business segments | segment									2
Contract revenues	$ 607,970	$ 607,901	$ 513,051	$ 518,470	$ 571,075	$ 583,214	$ 448,776	$ 468,094	$ 2,247,392	$ 2,071,159	$ 1,531,169
Identifiable assets	995,859				1,007,871				995,859	1,007,871
C&I
Segment Reporting Information [Line Items]
Contract revenues									1,093,014	936,748	638,061
Canada
Segment Reporting Information [Line Items]
Identifiable assets	$ 23,200				$ 24,800				23,200	24,800
Canada | C&I
Segment Reporting Information [Line Items]
Contract revenues									$ 77,900	$ 79,500	$ 53,800