Collaborative Arrangements and Acquisitions - CRISPR Therapeutics AG (Details) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2015 USD ($) target
CRISPR Therapeutics AG
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, investment in collaborative partner, pursuant to convertible loan agreement				30.0
Collaborative arrangement, development and regulatory potential milestone payments maximum				$ 420.0
Prior to marketing approval, time period of notice required to terminate (in days)				90 days
Subsequent to marketing approval, time period of notice required to terminate (in days)				270 days
CTX001 Co-Co
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research and development expenses		$ 5.2	$ 14.1
Preferred Stock | CRISPR Therapeutics AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement, investment in collaborative partner, pursuant to convertible loan agreement	$ 46.9
Common Stock | CRISPR Therapeutics AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Fair value of investment		$ 207.0	$ 207.0