Collaboration and License Agreements - Baxalta Collaboration Agreement (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) collaboration_project deliverable $ / shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development revenue	$ 18,378	$ 5,805	$ 5,738	$ 5,050	$ 4,583	$ 5,129	$ 25,595	$ 5,840
Baxalta Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of additional follow-on biologic products for development and product licenses | collaboration_project									4
Upfront payment paid by Baxter to the company									$ 33,000
Option payment which the entity is no longer eligible to receive									7,000
Option payments agreed to be paid by Baxter with respect to additional product candidates									12,000
One time cash payment	$ 51,200
Additional payment to be paid									28,000
Research and development revenue									22,000
Impact on performance period									$ 11,000
Change in performance period (in dollars per share) | $ / shares									$ 0.16
Accounting Standards Update 2009 to 2013 | Baxalta Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of additional follow-on biologic products for research and development services | collaboration_project									4
Total arrangement consideration									$ 61,000
Portion of revised arrangement consideration allocated to the first initial product license as a result of termination of product									10,300
Portion of revised arrangement consideration allocated to each of the three additional product licenses as a result of termination of product									10,300
Portion of revised arrangement consideration allocated to the second initial product license as a result of termination of product									9,400
Portion of revised arrangement consideration allocated to the joint steering committee unit of accounting as a result of termination of product									$ 114,000
Number of significant deliverables identified in arrangement | deliverable									7
Number of deliverables | deliverable									2
Portion of revised arrangement consideration reallocated to the remaining deliverables									$ 61,000
Decrease in portion of revised arrangement consideration reallocated to the remaining deliverables									$ 40,000