Collaborative Arrangements - Cystic Fibrosis Foundation Therapeutics Incorporated (Details) - USD ($)	1 Months Ended	3 Months Ended									12 Months Ended
	Apr. 30, 2011	Mar. 31, 2016	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	Dec. 31, 2012
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenues			$ 5,054,000	$ 1,546,000	$ 611,000	$ 842,000	$ 10,829,000	$ 33,502,000	$ 3,087,000	$ 4,257,000	$ 8,053,000	$ 51,675,000	$ 217,738,000
Cystic Fibrosis Foundation Therapeutics Incorporated
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative funding	$ 75,000,000
Number of years over which funding will be made (in years)	5 years
Collaborative revenues											$ 0	$ 6,500,000	14,300,000
Milestone payment made			$ 13,900,000										$ 9,300,000	$ 9,300,000
Scenario, Forecast | Cystic Fibrosis Foundation Therapeutics Incorporated
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment made		$ 13,900,000