Quarterly Financial Data (unaudited) (footnotes) (Details) - USD ($)		3 Months Ended
	Oct. 26, 2015	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expenses, early-stage research assets			$ 10,000,000
Moderna Therapeutics, Inc.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Up-front payment		$ 20,000,000.0
CRISPR Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative funding with CRISPR	$ 75,000,000			$ 75,000,000.0