Costs and estimated earnings in excess of billings (Details) (USD $)	Sep. 30, 2014		Dec. 31, 2013
Costs and estimated earnings in excess of billings [Abstract]
Unbilled costs and profits incurred to date	$ 261,435,000	[1]	$ 204,276,000	[1]
Unapproved change orders	137,985,000		146,787,000
Claims	320,757,000		222,185,000
Costs and estimated earnings in excess of billings	720,177,000		573,248,000
Unapproved change orders and claims subject to pending litigation	$ 38,400,000		$ 58,800,000

[1] Represents the excess of contract costs and profits recognized to date on the percentage of completion accounting method over the amount of contract billings to date on certain contracts.