Fair value of financial instruments - Cash, cash equivalents and marketable securities (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2022 USD ($) security	Jun. 30, 2022 USD ($) security
Net Investment Income [Line Items]
Cost	$ 87,698	$ 87,698
Gross Unrealized Losses	(92)	(92)
Estimated Fair Value	$ 87,606	$ 87,606
Number of debt securities | security	17	17
Other-than-temporary impairments	$ 0	$ 0
Cash and cash equivalents
Net Investment Income [Line Items]
Cost	46,882	46,882
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	$ 46,881	$ 46,881
Number of debt securities | security	2	2
Fair value of debt securities classified as cash and cash equivalents	$ 3,994	$ 3,994
Marketable securities
Net Investment Income [Line Items]
Cost	40,816	40,816
Gross Unrealized Losses	(91)	(91)
Estimated Fair Value	40,725	40,725
U.S. Treasury securities due in one year or less
Net Investment Income [Line Items]
Cost	40,816	40,816
Gross Unrealized Losses	(91)	(91)
Estimated Fair Value	$ 40,725	$ 40,725