Summary of Significant Accounting Policies - Inventory (Details)	6 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)
Summary of Significant Accounting Policies
Unbilled partner milestone	$ 5,000,000		$ 5,000,000
Inventory
Raw materials	357,000	$ 40,000	357,000
Work in process	1,835,000	998,000	1,835,000
Total	2,192,000	$ 1,038,000	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
Raw materials inventory write-downs		$ 1,100,000	1,100,000
Reserve for work in process	0	$ 0	$ 0
Rolling period of firm, fixed orders for conjugate that the company is required to manufacture		6 months
Rolling period of manufacturing projections for the quantity of conjugate the collaborator expects to need		12 months
Maximum period of firm, fixed orders and/or projections from collaborators considered for capitalizing inventory		12 months
Charges to research and development expense related to raw material inventory identified as excess	$ 150,000	$ 403,000		$ 1,100,000	$ 1,000,000