Contract Assets and Liabilities Changes in Net Contract Assets (Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Contract assets
Contract asset, current	$ 1,339	$ 1,145
Contract asset, non-current	397	188
Contract asset	1,736	1,333
Contract Liabilities
Contract liability, current	3,929	5,963
Contract liability, non-current	434	1,401
Contract liabilities	$ 4,363	$ 7,364