Collaborative Arrangements and Acquisitions - CRISPR Therapeutics AG (Details) - CRISPR Therapeutics AG $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2018 USD ($)	Dec. 31, 2015 USD ($) target	Jun. 30, 2018 USD ($)
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
Preferred Stock
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement, investment in collaborative partner, pursuant to convertible loan agreement	$ 21.5
Common Stock
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Fair value of investment			$ 242.8