Short-term and long-term investments - Additional Information (Details) - Investments in mutual funds and common stock - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Equity Securities, FV-NI, Gain (Loss)	$ 3,818	$ 4,383
Equity Securities, FV-NI, Realized Gain (Loss)	1,941	1,459
Net Increase (Decrease) In Unrealized Gains On Equity Securities	$ 1,877	$ 2,924