Revenue Net contract assets (liabilities) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jan. 01, 2018
Net contract assets (liabilities) [Abstract]
Contract with Customer, Asset, Gross, Current	$ 476	$ 4,604
Contract with Customer, Asset, Explanation of Change	-4128
Contract with Customer, Liability, Current	$ (962)	0
Contract with Customer, Liability, Explanation of Change	-962000
Contract with Customer, Asset, Net, Current	$ (486)	$ 4,604
Contract with Customer, Net, Explanation of Change	$ (5,090)