Summary of Significant Accounting Policies (Costs and Estimated Earnings in Excess of Billings) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Summary of Significant Accounting Policies [Abstract]
Claims	$ 477,425	$ 407,164
Unapproved change orders	207,475	270,019
Other unbilled costs and profits	146,926	227,992
Total costs and estimated earnings in excess of billings	$ 831,826	$ 905,175