Income taxes - Current income tax provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current income tax provision:
Income tax benefit related to operating losses and research and development tax credits	$ 0	$ 0	$ 0
State			24
Total current income tax provision			24
Deferred income tax benefit:
Federal	23,352	(17,580)	(9,400)
State	7,274	(3,135)	688
Total deferred income tax benefit	30,626	(20,715)	(8,712)
Change in deferred tax asset valuation allowance	$ (30,626)	$ 20,715	8,712
Income tax benefits			$ 24