Commitments and Contingencies - Legal (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Feb. 25, 2015	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Commitments and contingencies
Revenue		$ 908,216	$ 789,929	$ 1,651,459	$ 1,451,487
Gross Profit		100,967	$ 80,531	148,777	$ 132,991
JCG | North Texas Tollway Authority v. James Construction Group, LLC
Commitments and contingencies
Expected remediation cost on settlement	$ 17,000
Remaining accrual balance		4,700		4,700
Expected remediation cost	22,400
Increase in liability				1,300
Remediation costs				5,100
JCG | North Texas Tollway Authority v. James Construction Group, LLC | Maximum
Commitments and contingencies
Agreed payments by second defendant in expected remediation costs toward settlement	$ 5,400
Bonding
Commitments and contingencies
Bid and completion bonds issued and outstanding		$ 710,600		$ 710,600		$ 648,600