Costs and estimated earnings in excess of billings (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Costs and estimated earnings in excess of billings
Unbilled costs and profits incurred to date	$ 291,188,000	$ 204,276,000
Unapproved change orders	163,921,000	146,787,000
Claims	243,314,000	222,185,000
Costs and estimated earnings in excess of billings	698,423,000	573,248,000
Unapproved change orders and claims subject to pending litigation	$ 58,800,000	$ 58,800,000