Collaborative Arrangements - Cystic Fibrosis Foundation Therapeutics Incorporated (Details) - USD ($)		3 Months Ended				9 Months Ended
	Oct. 13, 2016	Sep. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenues		$ 259,000			$ 1,546,000	$ 1,008,000	$ 2,999,000
Cystic Fibrosis Foundation Therapeutics Incorporated
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone Payments				$ 13,900,000
Milestone Revenues			$ 13,900,000
Additional Milestone Payments						$ 0
Subsequent Event | Cystic Fibrosis Foundation Therapeutics Incorporated
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative funding	$ 75,000,000.0
Additional Collaborative Funding	$ 6,000,000.0