Accounting Policies (Schedule of Accounts Receivable) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Trade and other accounts receivable	$ 146,460	$ 123,179
Bank promissory notes	15,759	15,845
Revenue in excess of progress billings	15,926	15,889
Allowance for doubtful accounts	(6,952)	(8,530)
Total accounts receivable	$ 171,193	$ 146,383