Convertible Notes - Promissory Notes Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Debt discount	$ (18,003)	$ (18,003)
Convertible Debt
Debt Instrument [Line Items]
Convertible promissory notes	18,003	18,003
Debt discount			$ (18,100)
Convertible promissory notes, net	0	0
Issued with September 2016 Convertible Notes
Debt Instrument [Line Items]
Debt discount	(9,598)	(9,598)	(9,600)
Compounded Bifurcated Derivatives
Debt Instrument [Line Items]
Debt discount	(1,267)	(1,267)	(1,300)
Beneficial Conversion Feature
Debt Instrument [Line Items]
Debt discount	$ (7,138)	$ (7,138)	$ (7,200)