Collaboration with GlaxoSmithKline Intellectual Property Development Limited (Details)	1 Months Ended	3 Months Ended			9 Months Ended
	Nov. 30, 2015 person	Sep. 30, 2017 USD ($)	Jun. 30, 2017	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($) item	Sep. 30, 2017 USD ($) agreement	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Alliance revenue		$ 164,000		$ 323,000				$ 729,000	$ 918,000
Current portion of deferred revenue		563,000			$ 563,000	$ 563,000	$ 563,000	563,000		$ 1,111,000
Long-term deferred revenue		94,000			94,000	$ 94,000	94,000	94,000		$ 152,000
Operating expenses		14,831,000		13,300,000				52,176,000	40,418,000
Operating expense
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Operating expenses		1,600,000		1,600,000				9,200,000	5,100,000
GSK Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Deferred revenue recognition period	36 months
Number of development candidates	1					1
Number of units of accounting in connection of agreements | item						2
Alliance revenue		100,000		$ 300,000				600,000	$ 800,000
Deferred revenue		700,000			700,000	$ 700,000	700,000	700,000
Research period			27 months
Current portion of deferred revenue		600,000			600,000	600,000	600,000	600,000
Long-term deferred revenue		$ 100,000			$ 100,000	$ 100,000	$ 100,000	100,000
Additional extended research period			36 months
GSK Agreement | Clinical and Commercial Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments								89
GSK Agreement | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Anticipated initial collaboration term	4 years
Number of optional additional targets						2	2
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								100,000,000
GSK Agreement | Maximum | Research and Development Plans and Designation of Development Candidates
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments								9
GSK Agreement | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Anticipated initial collaboration term	2 years
R&D Services Unit of Accounting | Up-front Payment Arrangement | GSK Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Upfront payment received under collaboration agreement								2,500,000
JSC Deliverable | Up-front Payment Arrangement | GSK Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Upfront payment received under collaboration agreement								$ 0