Costs and estimated earnings in excess of billings (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Costs and estimated earnings in excess of billings
Unbilled costs and profits incurred to date	$ 170,088,000	$ 157,119,000
Unapproved change orders	133,523,000	141,596,000
Claims	175,750,000	166,287,000
Costs and estimated earnings in excess of billings	479,361,000	465,002,000
Unapproved change orders and claims subject to pending litigation	$ 62,500,000	$ 62,000,000