Collaboration and License Agreements (Details) $ in Millions	1 Months Ended		3 Months Ended
	Nov. 30, 2016 USD ($) director	Nov. 30, 2015 USD ($) person	Mar. 31, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Total number of board of director seats | director	7
Number of common board of directors | director	0
Baker Bros. Advisors LP
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Common stock ownership percentage under the collaboration agreement	7.00%
Number of board director seats held | director	2
Vivelix
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Remaining performance obligation			$ 0.0
Total number of board of director seats | director	4
Number of common board of directors | director	0
Vivelix | Up-front Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Upfront payment received under collaboration agreement	$ 15.0
Vivelix | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments	$ 140.0
Vivelix | Maximum | Back-up compounds
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Anticipated initial collaboration term	3 years
Milestone payments	$ 52.5
Vivelix | Maximum | Development and Regulatory Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments	65.0
Vivelix | Maximum | Development and Regulatory Milestones | Back-up compounds
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments	35.0
Vivelix | Maximum | Sales Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments	75.0
Vivelix | Maximum | Sales Milestones | Back-up compounds
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments	$ 17.5
GSK Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Deferred revenue recognition period		36 months
Number of optional additional targets | person		2
Number of development candidates | person		1
Remaining performance obligation			$ 0.0
Revised, increased research period			36 years
GSK Agreement | Up-front Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Upfront payment received under collaboration agreement		$ 2.5
GSK Agreement | License, Research, Clinical Development and Commercialization
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments			$ 20.0
GSK Agreement | Research and Development Plans and Designation of Development Candidates
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments			1.0
GSK Agreement | Clinical and Commercial Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments		$ 89.0	$ 17.0
GSK Agreement | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Anticipated initial collaboration term		4 years
Maximum royalty percentage on net sales			5.00%
GSK Agreement | Maximum | License, Research, Clinical Development and Commercialization
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments		$ 100.0
GSK Agreement | Maximum | Research and Development Plans and Designation of Development Candidates
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments		$ 9.0
GSK Agreement | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Anticipated initial collaboration term		2 years
R&D Services Unit of Accounting | GSK Agreement | Up-front Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Upfront payment received under collaboration agreement		$ 2.5