Stockholders' equity - Narrative (Details)	Dec. 31, 2021 vote shares	Nov. 30, 2021 $ / shares shares	Nov. 03, 2021 shares	Dec. 31, 2020 shares
Subsidiary, Sale of Stock [Line Items]
Common stock, shares authorized (in shares)	200,000,000			0
Common stock, number of votes (in votes per share) | vote	1
Common stock, shares issued (in shares)	23,585,000			0
Common stock, shares outstanding (in shares)	23,585,000		0	0
Preferred stock, shares authorized (in shares)	10,000,000			0
Preferred stock, shares issued (in shares)	0			0
Preferred stock, shares outstanding (in shares)	0			0
Private Placement | Bluebird Bio
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued (in shares)		23,368,988
Pre-funded Warrants | Private Placement
Subsidiary, Sale of Stock [Line Items]
Pre-funded warrants issued (in shares)		757,575
Exercise price of warrants (in dollars per share) | $ / shares		$ 0.0001