Collaborative Arrangements and Acquisitions - CRISPR Therapeutics AG (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2015 USD ($) target
CRISPR Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Right to license, number of targets (up to) | target			6
Collaborative arrangement, up-front payment			$ 75.0
Collaborative arrangement, development and regulatory potential milestone payments maximum			$ 420.0
CTX001 Co-Co
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research and development expenses	$ 7.0	$ 3.6