Summary of Significant Accounting Policies - Inventory (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) item	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Summary of Significant Accounting Policies
Unbilled partner milestone					$ 5,000,000
Inventory
Raw materials	$ 124,000		$ 124,000		357,000
Work in process	2,119,000		2,119,000		1,835,000
Total	2,243,000		$ 2,243,000		$ 2,192,000
Number of suppliers | item			2
Minimum supply period of raw materials that is not supported by firm, fixed orders and/or projections from collaborators considered to expense inventory			12 months
Value of excess inventory	0		$ 0
Raw materials inventory write-downs	0	$ 0	403,000	$ 152,000
Reserve for work in process	$ 0		$ 0