Collaboration and License Agreements - Mylan Collaboration Agreement (Details) $ in Thousands		12 Months Ended
	Jan. 08, 2016 USD ($)	Dec. 31, 2017 USD ($) milestone_payment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Commercial milestone		$ 10,000		$ 20,000
Mylan Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment	$ 45,000
Milestone payment on collaboration agreement	200,000
Cash received from milestone payments			$ 60,000
Number of years for ceasing agreement		2 years
Commercial milestone		$ 0
Payments for milestones applied to cost share percentage		8,200
Amount of offset against research and development costs		$ 24,700	$ 27,100
Percentage of cost sharing arrangement under collaborative and license agreements		50.00%
Number of milestone payments | milestone_payment		2
Amount of offset against general and administrative costs		$ 1,200
Accounting Standards Update 2009 to 2013 | Mylan Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total arrangement consideration	45,000
Portion of revised arrangement consideration allocated to the first initial product license as a result of termination of product	8,200
Portion of revised arrangement consideration allocated to the joint steering committee unit of accounting as a result of termination of product	51
Deferred revenue amortized to research and development revenue		33,600
Deferred revenue included in current liabilities		2,900
Deferred revenue included in non-current liabilities		$ 30,700
Minimum | Accounting Standards Update 2009 to 2013 | Mylan Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of revised arrangement consideration allocated to each of the three additional product licenses as a result of termination of product	5,700
Revenue Recognition, Multiple-deliverable Arrangements, Performance Period for Unit of Accounting		5 years
Maximum | Accounting Standards Update 2009 to 2013 | Mylan Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of revised arrangement consideration allocated to each of the three additional product licenses as a result of termination of product	$ 9,000
Revenue Recognition, Multiple-deliverable Arrangements, Performance Period for Unit of Accounting		8 years