Income Taxes - Uncertain tax positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Balance at the beginning of the year	$ 486	$ 213
Increase based on current year tax positions	254	271
Increase (decrease) for prior year tax positions	(206)	2
Balance at the beginning of the year	$ 534	$ 486