Collaboration Agreements (Intellia Therapeutics) (Details) - USD ($)	1 Months Ended	6 Months Ended	12 Months Ended
	Apr. 30, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Collaboration Agreements [Line Items]
Payments to Acquire Marketable Securities			$ 1,277,140,000	$ 809,419,000	$ 557,105,000
Intella Therapeutics [Member]
Collaboration Agreements [Line Items]
Upfront Payment Made	$ 75,000,000
Payments to Acquire Marketable Securities		$ 50,000,000.0