Costs and estimated earnings in excess of billings (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Costs and estimated earnings in excess of billings
Unbilled costs and profits incurred to date	$ 196,308,000	$ 157,119,000
Unapproved change orders	144,839,000	141,596,000
Claims	197,274,000	166,287,000
Costs and estimated earnings in excess of billings	538,421,000	465,002,000
Unapproved change orders and claims subject to pending litigation	$ 54,100,000	$ 62,000,000