Patent License Agreement - Narrative (Details) £ in Millions			1 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2018 GBP (£)	Dec. 31, 2017 USD ($)	Aug. 31, 2017 USD ($)	Jan. 31, 2017 GBP (£) shares	Jan. 31, 2017 USD ($) shares	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Finite-Lived Intangible Assets [Line Items]
One-time upfront payment for finite-lived intangible asset								$ 0	$ 1,102,000
Patent Licensing Agreement
Finite-Lived Intangible Assets [Line Items]
One-time upfront payment for finite-lived intangible asset				£ 1.0	$ 1,100,000
Milestone payment			$ 1,200,000	£ 1.0
Future royalty payments | £	£ 13.4
Capitalized license fees		$ 8,739,000			$ 6,300,000	$ 8,044,000		8,044,000
Useful life (years)	8 years 3 months 18 days	9 years
Amortization of Intangible Assets						$ 266,000	$ 232,000	$ 694,000	$ 674,000
Series D Convertible Preferred Stock | Patent Licensing Agreement
Finite-Lived Intangible Assets [Line Items]
Stock issued during period for purchase of asset, shares | shares				141,774	141,774
Fair value of stock issued for purchase of license agreement					$ 1,100,000
Discount Rate
Finite-Lived Intangible Assets [Line Items]
Debt security, measurement input					0.15