Summary of Significant Accounting Policies - Inventory (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Inventory
Raw materials	$ 40,000		$ 40,000
Work in process	328,000		998,000
Total	$ 368,000		$ 1,038,000
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
Raw materials inventory write-downs	0	$ 403,000
Reserve for work in process	0
Difference between full cost and amounts received	$ 344,000	$ 727,000