Collaborative Arrangements - CRISPR Therapeutics AG (Details) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Jul. 31, 2019	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Investment in collaborative partner, pursuant to convertible loan agreement				$ 63,300,000	$ 46,900,000	$ 8,700,000
CRISPR Therapeutics
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative funding		$ 30,000,000.0
Collaborative arrangement development and regulatory potential milestone payments maximum	$ 825,000,000.0			410,000,000.0
Collaborative arrangement, development and commercialization rights potential maximum milestone payments			$ 175,000,000.0
CTX001 Co-Co Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative arrangement research and development expenses				$ 30,100,000	$ 19,700,000