Collaborative Arrangements (Details)	1 Months Ended		3 Months Ended				9 Months Ended
	Sep. 30, 2020 USD ($)	Jul. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) target	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
CRISPR Therapeutics
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative arrangement, right to exclusively license, number of targets | target					3
Collaborative arrangement, development and regulatory potential milestone payments maximum					$ 410,000,000.0
CTX001 Co-Co
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative arrangement research and development expenses			$ 14,300,000			$ 7,700,000	$ 33,400,000	$ 22,300,000
CRISPR DMD/DM1
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative arrangement, development and regulatory potential milestone payments maximum				$ 800,000,000.0
Collaborative arrangement research and development expenses				$ 25,000,000.0
Collaborative arrangement, up-front payment paid		$ 175,000,000.0
Moderna, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative arrangement, development and regulatory potential milestone payments maximum	$ 380,000,000.0
Collaborative arrangement, up-front payment paid	$ 75,000,000.0