Costs and estimated earnings in excess of billings (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Costs and estimated earnings in excess of billings
Unbilled costs and profits incurred to date	$ 283,516,000	$ 204,276,000
Unapproved change orders	125,018,000	146,787,000
Claims	252,418,000	222,185,000
Costs and estimated earnings in excess of billings	660,952,000	573,248,000
Unapproved change orders and claims subject to pending litigation	$ 20,500,000	$ 58,800,000