Income Taxes - Effective income tax rate reconciliation, Amount (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income tax expense benefit reconciliation
Federal income tax at statutory rate	$ (6,233)	$ (4,642)
State income tax, net of federal benefit	(1,293)	(1,300)
Foreign tax differential	2,346	733
Permanent differences	394	178
Tax credits generated in current year	(732)	(783)
Other	840	1
Valuation allowance	$ 4,678	$ 5,813