Leases - Operating leases in consolidated balance sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases
Right-of-use asset	Operating lease assets	Operating lease assets
Operating lease assets	$ 103	$ 182
Current operating lease liabilities	$ 81	$ 107
Current portion of operating lease liabilities	Current operating lease liabilities	Current operating lease liabilities
Non-current operating lease liabilities	$ 22	$ 75
Operating lease liabilities, net of current portion	Non-current operating lease liabilities	Non-current operating lease liabilities
Total operating lease liabilities	$ 103	$ 182