Cash and cash equivalents and marketable securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Cash and cash equivalents:
Cash	$ 4,712		$ 6,061
Money market accounts	141,204		34,340
Total cash and cash equivalents	145,916		40,401
Short-term marketable securities-available-for-sale:
Marketable securities	29,301		40,214
Total short-term marketable securities	29,301		$ 40,214
Interest income	$ 296	$ 714