Collaborative Arrangements and Acquisitions - CRISPR Therapeutics AG (Details)	1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($) target	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Fair Value				$ 1,812,248,000	$ 1,434,557,000
Gross unrealized gains				13,740,000	$ 21,422,000
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			$ 75,000,000
Collaborative arrangement, investment in collaborative partner, pursuant to convertible loan agreement			30,000,000
Collaborative funding			75,000,000
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
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		$ 3,100,000
Common Stock | CRISPR Therapeutics AG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement, investment in collaborative partner, pursuant to convertible loan agreement	$ 10,000,000
Fair Value				56,900,000
Gross unrealized gains				$ 13,700,000