Quarterly Financial Data (unaudited) Quarterly Financial Data (unaudited) (footnotes) (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended								12 Months Ended
	Oct. 26, 2015	Apr. 30, 2014	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Restructuring charges			$ 1,524	$ 1,826	$ 2,128	$ (3,272)	$ 4,164	$ 40,843	$ (270)	$ 6,188	$ 2,206	$ 50,925	$ 40,521
One-time cash payment from landlord pursuant to Fan Pier Leases		$ 36,700
CRISPR Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative funding with CRISPR	$ 75,000
Janssen
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Up-front payment								$ 30,000				$ 35,000