Contract Assets and Liabilities Changes in Net Contract Assets (Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Contract assets
Contract asset, current	$ 892	$ 1,145
Contract asset, non-current		188
Contract asset	892	1,333
Contract Liabilities
Contract liability, current	6,379	5,963
Contract liability, non-current	576	1,401
Contract liabilities	$ 6,955	$ 7,364