Collaboration Agreements (Intellia Therapeutics) (Details)	1 Months Ended	6 Months Ended	12 Months Ended
	Apr. 30, 2016 USD ($) target	Jun. 30, 2016 USD ($) shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Collaboration Agreements [Line Items]
Payments to Acquire Marketable Securities			$ 809,419,000	$ 557,105,000	$ 564,188,000
Intella Therapeutics [Member]
Collaboration Agreements [Line Items]
Upfront Payment Made	$ 75,000,000
Collaboration Agreement, Number of Targets Company Has Rights To | target	10
Collaboration Agreement, Extension Period	2 years
Investment obligation		$ 50,000,000
Shares of Common Stock Purchased | shares		2,777,777
Payments to Acquire Marketable Securities		$ 50,000,000.0