Commitments and Contingencies (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Feb. 25, 2015	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2014
Commitments and contingencies
Billings in excess of costs and estimated earnings		$ 158,698		$ 158,698		$ 112,606
Revenue		631,165	$ 456,811	1,192,667	$ 887,257
Gross Profit		84,483	$ 43,285	139,536	$ 82,562
Withdrawal liability recorded		5,100		5,100
Construction Project One
Commitments and contingencies
Receivable recorded relating to the project							$ 32,900
Billings in excess of costs and estimated earnings		17,800		17,800
JCG | North Texas Tollway Authority v. James Construction Group, LLC
Commitments and contingencies
Settlement	$ (9,000)
Defendants paid to remove the liability	8,000
Expected remediation cost	22,400
Estimated cost of remediating issues for lawsuit		17,000		17,000
Remaining accrual balance		$ 14,500		$ 14,500
Percentage of expected costs second defendant would pay		20.00%		20.00%
Percentage of expected costs Company would pay		80.00%		80.00%
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
Letters of credit
Commitments and contingencies
Total commercial letters of credit outstanding		$ 15,700		$ 15,700		16,200
Bonding
Commitments and contingencies
Bid and completion bonds issued and outstanding		$ 1,460,000		$ 1,460,000		$ 1,530,000