Costs and estimated earnings in excess of billings (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Costs and estimated earnings in excess of billings
Unbilled costs and profits incurred to date	$ 200,430,000	$ 157,119,000
Unapproved change orders	118,811,000	141,596,000
Claims	185,670,000	166,287,000
Costs and estimated earnings in excess of billings	504,911,000	465,002,000
Unapproved change orders and claims subject to pending litigation	$ 62,900,000	$ 62,000,000