Contract Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Contract assets	$ 42,895
Increase decrease in contract assets	2,116
Increase decrease in contract liabilities	2,300
Revenue recognized	1,000
Accounts Receivable [Member]
Contract assets	$ 44,900