Collaborative Arrangements - CRISPR Therapeutics AG (Details)	1 Months Ended		3 Months Ended	12 Months Ended
	Jan. 31, 2018 USD ($)	Oct. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($) target	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Fair Value					$ 2,088,666,000	$ 1,434,557,000
Gross Unrealized Gains					31,608,000	$ 21,422,000
CRISPR Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Right to license, number of targets (up to) | target				6
Collaborative funding				$ 75,000,000.0
Investment in collaborative partner, pursuant to convertible loan agreement		$ 10,000,000	$ 3,100,000	30,000,000
Collaborative arrangement development and regulatory potential milestone payments maximum				$ 420,000,000
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
CRISPR Therapeutics | Subsequent Event
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Investment in collaborative partner, pursuant to convertible loan agreement	$ 21,500,000
Common Stock | CRISPR Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Fair Value					74,800,000
Gross Unrealized Gains					$ 31,600,000