Costs and estimated earnings in excess of billings (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Costs and estimated earnings in excess of billings [Abstract]
Claims	$ 395,708	$ 407,164
Unapproved change orders	224,297	270,019
Other unbilled costs and profits	238,351	227,992
Total costs and estimated earnings in excess of billings	$ 858,356	$ 905,175