Contract Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Contract assets	$ 59,244		$ 59,244
Increase decrease in contract assets	(13,877)		(11,761)
Increase decrease in contract liabilities			3,500
Revenue recognized			1,000
Accounts Receivable [Member]
Contract assets	$ 47,400		$ 47,400