Revenue recognition - Collaboration and Royalty Revenue (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Aug. 31, 2021	Mar. 31, 2021	Nov. 30, 2011
Collaboration and royalty revenue
Remaining potential milestones that can be achieved	$ 250,000	$ 250,000		$ 250,000
Revenue		217,127	$ 138,743	531,389	$ 373,364
Collaboration revenue
Collaboration and royalty revenue
Revenue		50,017	10,011	50,024	30,018
Royalty revenue
Collaboration and royalty revenue
Revenue		32,924	13,127	73,645	33,348
SMA License Agreement \| Collaboration revenue
Collaboration and royalty revenue
Revenue		50,000	10,000	50,000	30,000
SMA License Agreement \| Royalty revenue
Collaboration and royalty revenue
Revenue		32,900	13,100	73,600	33,300
SMA License Agreement \| Roche And Sma Foundation \| Collaboration revenue
Collaboration and royalty revenue
Revenue		50,000	10,000	50,000	30,000
Research And Development Event Milestones \| SMA License Agreement
Collaboration and royalty revenue
Remaining potential milestones that can be achieved	0	0		0
Milestone payments received			10,000		10,000
Sales Milestones \| SMA License Agreement
Collaboration and royalty revenue
Remaining potential milestones that can be achieved	250,000	$ 250,000		$ 250,000
Milestone payments received			$ 20,000		$ 20,000	$ 10,000	$ 20,000
Net sales milestone threshold achieved	750,000
Sales Milestones \| SMA License Agreement \| Prepaids and other current assets
Collaboration and royalty revenue
Milestone payments due	$ 50,000
Maximum \| Research And Development Event Milestones \| SMA License Agreement
Collaboration and royalty revenue
Remaining potential milestones that can be achieved								$ 135,000
Maximum \| Sales Milestones \| SMA License Agreement
Collaboration and royalty revenue
Remaining potential milestones that can be achieved								$ 325,000