Research and Collaboration Agreements - Pfizer Inc - Additional Information (Details) - Collaborative Arrangement - Pfizer Inc	1 Months Ended			12 Months Ended
	May 31, 2016	Dec. 31, 2014 USD ($)	May 31, 2013 USD ($) Target SaleIndicator	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of research targets | Target			2
Nominated number of additional research targets | Target			2
Deferred revenue				$ 3,400,000	$ 4,900,000
Estimated performance period of agreement			7 years
Additional target as deferred revenue		$ 1,500,000
Adjusted amortization period of deferred revenue	5 years 6 months
Revenue recognized from collaborative arrangement				2,200,000	1,800,000	$ 2,300,000
Amount due from agreement				$ 100,000	$ 400,000
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable			$ 263,500,000
Exercise of License Options [Member] | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable			4,500,000
Achievement Of Development Milestones For Each Research Target Program | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable			38,000,000
Achieving First Commercial Sale In Various Territories | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable			$ 101,000,000
Number of sales indicators | SaleIndicator			3
Achieving Sales Milestones For Each Research Target Program | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable			$ 120,000,000
Up Front Payment Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			6,000,000
Deferred revenue			$ 6,000,000