Cash and cash equivalents and marketable securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and cash equivalents:
Cash	$ 15,286	$ 6,061
Money market funds	20,825	34,340
Total cash and cash equivalents	36,111	40,401
Short-term marketable securities-available-for-sale:
Marketable securities	4,565	40,214
Total short-term marketable securities	4,565	40,214
Interest income	$ 588	$ 2,012	$ 742