Organization and Basis of Presentation (Details) - USD ($)			1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 25, 2019	May 10, 2017	Jan. 31, 2017	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit				$ (490,011,000)	$ (490,011,000)		$ (475,667,000)
Cash and cash equivalents and investments				20,700,000	20,700,000
Restricted cash				500,000	500,000		$ 500,000
Line of Credit Facility [Line Items]
Amount of equity able to raise			$ 200,000,000
Maximum offering price		$ 50,000,000
Net proceeds from issuance of common stock					3,000,000	$ 21,324,000
Issuance of common stock				$ 3,000,000	$ 3,000,000	$ 21,325,000
Equity Distribution Agreement
Line of Credit Facility [Line Items]
Number of shares sold (in shares)					785,280
Net proceeds from issuance of common stock					$ 1,500,000
Innovatus
Line of Credit Facility [Line Items]
Issuance of common stock	$ 3,000,000
Term loan | 2019 Secured Loan Agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 30,000,000