Contract Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Contract assets	$ 56,100		$ 56,100
Increase decrease in contract assets	3,040		(8,721)
Increase decrease in contract liabilities			5,600
Revenue recognized			1,000
Accounts Receivable [Member]
Contract assets	$ 47,400		$ 47,400