Commitments and Contingencies - Legal (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Feb. 25, 2015	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Commitments and contingencies
Revenue		$ 789,778	$ 865,064	$ 789,929	$ 661,558	$ 877,670	$ 908,902	$ 648,787	$ 504,119	$ 3,106,329	$ 2,939,478	$ 2,379,995
Gross Profit		$ 89,514	$ 108,421	$ 80,531	$ 52,460	103,253	$ 106,505	$ 71,419	$ 44,560	$ 330,926	325,737	$ 278,434
Construction Project One
Commitments and contingencies
Receipts related to disputed receivable											32,900
Revenue											18,100
Gross Profit											17,400
JCG | North Texas Tollway Authority v. James Construction Group, LLC
Commitments and contingencies
Expected remediation cost on settlement	$ 17,000
Percentage of expected costs second defendant would pay		20.00%								20.00%
Percentage of expected costs Company would pay		80.00%								80.00%
Remaining accrual balance		$ 8,500								$ 8,500
Expected remediation cost	22,400
Increase in liability										1,600
Remediation costs										11,600
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		$ 648,600				$ 554,900				$ 648,600	$ 554,900