Leases - Operating lease assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Leases [Abstract]
Non-current operating lease assets	$ 1,386
Operating lease liabilities:
Current operating lease liabilities	1,135
Non-current operating lease liabilities	397
Total operating lease liabilities	$ 1,532	$ 2,887